In this case, all the successor activities of the EST activity start at their earliest time because one EST activity affects all the upcoming activities. Similarly, all successors finish at their earliest finish time. The latest start time means the time when an activity can start as late as possible without impacting the deadline of the project. This happens when an activity starts at its late start time and all the successors of that activity become LST activities.
The earliest finish time means the time when an activity finishes as early as possible. In this scenario, all the successor activities become EFT activities. Similarly, all successors start at their earliest start time. The latest finish time is the time when an activity finishes as late as possible without affecting the overall project deadline. In this case, the successor activities start at their latest start time and finish at their latest finish time. Note: It is necessary to remember that there occur only a single longest path in the network and the other paths are being shorter than that length or equal to that length.
Therefore, the activities and events should finish before the actual required time. Seven weeks are required to go from event 2 to event 5 on the critical path by taking the route 2, 3, 5. Only four weeks are needed if the route 2, 4, 5 is adopted. Therefore three weeks are required if route is adopted. Therefore event 4 should begin anywhere between zero to three weeks because it needs two weeks for completion after event 2 is completed.
Another use for resources of people, facilities, money, and equipment needed to finish event 4 must be searched by the management during these three weeks. Therefore for resource allocation and scheduling as the critical path is important, because those events that are not on the critical path for achievement can be rescheduled by the project manager with the coordination from the functional manager, during other time periods when maximum utilization of resources can be accomplished under the provision that the critical path time is not extended.
A better balance of resources throughout the company is provided by this type of rescheduling through the utilization of slack times. Even by eliminating waiting or idle time, project costs may possibly reduce. We can calculate the slack time easily for each activity by using a simple formula which is given below. This formula indicates that the slack time is equal to the difference between the latest permit able date and the earliest expected date based on the following nomenclature is said to be slack.
Here is the formula. This formula is also known as Activity Slack Formula. It means the activity slack also refers to the length of the time an activity can be delayed without delaying the project deadline. Another formula for calculating slack time is to subtract the latest finish time from early finish time which is in the form of the formula:.
In simplest words, the slack time is the difference between the time allocated to the task and the time it actually takes. For example, if you allocate 20 days to a task but the task is finished in 15 days then the slack or float time is 5 days. Suppose Christina is a chef at a famous five-star hotel and she is assigned a project on 15th October to introduce a completely new recipe for the customers.
She is given the deadline of 15th November. Before she prepares the recipe, she has to collect the ingredients that meet the specifications of the recipe.
So, her first task is to collect ingredients with certain nutritional values. Now Christina starts to calculate the slack time for her first task which is collecting ingredients. The deadline for this task is 2nd November. Christina finds that the earliest start time is the 10th of October and the latest start time is the 25th of October. So, the slack time for collecting ingredients with specific nutrition is 15 days. It means Christina has 15 days to finish this task. This is a simple slack time example that explains this term well.
The calculation for slack time is conducted for every event in the network as shown in the following figure by recognizing the latest starting date and the earliest expected date. The reference point for the network can be served as event 1 and can be easily specified as a calendar date. The bold line represents the critical path as before. There is no slack i. The critical path is terminated by event 6 with a completion time of 15 weeks.
By subtracting the time needed to finish the activity from events 3 to 5 from the latest beginning date of event 5 the latest allowable date is acquired. Now event 3 may happen anywhere between weeks 2 and 5 without disturbing the planned finishing date of the project. A simple PERT network is included in the above-mentioned diagram and therefore slack time calculation is not much difficult.
The earliest beginning dates should be ascertained by proceeding from start to completion through the network, for complex networks including multiple paths. Similarly, by working backward from completion to beginning, the latest allowable beginning date can be calculated.
It should be cleared that the significance of recognizing clearly where the slack persistence cannot be overstated. Better technical performance is permitted by the effective use of slack time. Because of slack times, PERT networks are mostly not plotted with a time scale. There can be a requirement for the planning requirements that the PERT charts be rebuilt with time scales, in which situation a decision should be taken either to wish late or early time requirements for slack variables.
The above figure represents this by comparing manpower planning with total program costs. In this figure, early time requirements for slack variables are used. The profitability of successfully meeting the schedule is ascertained by combining the earliest time and late time. In the table below, a sample of the needed information is highlighted. The latest and earliest times are regarded as random variables.
The actual schedule indicates the schedule for event occurrences that were built at the start of the project. In this table, the last column provides the profitability regarding the earliest time that will not surpass the actual schedule time for a specific event.
In the example represented above, for every event, the latest times and earliest times were calculated. The earliest and latest times were preferably evaluated for every activity instead.
Additionally, the latest and earliest times were recognized merely as the date or time when an event may be anticipated to occur. A forward pass through the network should be made to evaluate the earliest starting times i. But as a project manager, you need to consider two primary factors when determining the best use of slack time. First, the project goals and how leveraging slack time can help you complete the project on schedule. Notice whether the speed of delivery needs to be changed — thus, the WIP limits corrected.
Do menial work that is normally avoided, like regular system maintenance. Or simply get spend the time thinking and produce some creative solutions and ideas. Continuous improvement, remember? So slack time will occur again, and it might be the best thing that can happen to your flow. Even of you want every spare moment to be filled with work I strongly advise you against it. But all productivity methods advise taking breaks. We need those breaks, like slack time, to do a couple of things.
And two, take a step back, look at the bigger picture and make sure we have the capacity to deal with planned and unexpected events. If having slack time and no predefined tasks to work on is freaking you out, you can try and add a slack time card to your board and fill it with a defined activity. Like actually taking a break, or spending the time learning and perfecting a new skill.
In instances when projects can only begin after your team finishes another task or element, you can establish the latest start date based on your project goals and timeline. The project manager in this case can establish April 8 as the latest start date for the project. Once you know your earliest and latest start times for your project, you can use the subtraction formula to determine the total slack time. Using the previous start dates, calculate the slack time when:.
The slack time in this example is four days, which means the example software development team has up to four days to begin the project after completing either a previous project or an individual process necessary to support the following development processes. Additionally, the slack time you calculate between the earliest and latest start dates must be equal to the difference between the earliest and latest completion times.
To ensure the slack time you calculate when subtracting your start times is equal to the time between your completion dates, use the same process to find the difference. Determine the earliest date that you expect your team to complete the project. In the example software development project, the earliest completion date is April Now, you can establish the latest project completion date.
Determine this deadline by adding your slack time to the earliest completion date for your project. Using the previous dates for the example software development project, add four days to the earliest completion date of April This gives the team until April 28 to complete the project. Likewise, the slack time between start and completion dates is equal to four. You can determine which projects and tasks are critical within a critical path project management outline, depending on the type of projects you complete.
Critical projects result in a slack time of zero, which indicates when a project requires immediate initiation. So long as your slack time is greater than zero, the projects or tasks you're calculating should not be critical. In situations when a project or task becomes critical, project managers can then take steps to implement techniques that support the completion of critical projects.
Related: 7 Steps for Defining a Project's Scope. For the following example, assume a project manager and their team has outlined a PERT chart with the following information:. Task name: Development Stage 2StartCompleteEarliest LatestAccording to the information in the chart, the team can start the second stage of their development project as early as three days after completing the first stage and as late as seven days after finishing the first stage.
It's important to remember that the slack time between start and completion times is the same.
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