This is the second part of a two-part article on Project Time Management. In the previous post, we started to examine Project Time Management by discussing the first four processes that make up the knowledge area. You can view the post here. In this post we will conclude the knowledge area by examining the develop schedule and control schedule processes. We will examine the inputs, tools and techniques, and outputs of these processes.
Okay, now that you have defined your activities, sequenced them, estimated the resources you need to implement them and have gone further to estimate how long it should take to carry out these activities, it is time to develop a project schedule. The schedule creation process actually places dates on the activities and milestones. You should note that this process is usually iterative; you might have to go back and forth with the project sponsor and the team before you can arrive at an acceptable schedule.
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In order to develop the schedule, you’ll require inputs from the previous processes we have discussed in time management. The activity list, attributes, project network diagram, resource requirements and duration estimates should be consulted when you are developing the schedule.
An important aspect of determining the project schedule is being able to identify the critical path of the project. The critical path of a project is the set of activities that cannot afford to be delayed without impacting the project schedule. Think about it this way: if you have a task that you cannot afford to slack on, then that task is critical.
So are there tasks that we can afford to delay a little without impacting the project? Yes. For example, if one of the tasks for the project is the procurement of packaging, even though the packaging takes 5 days to procure, they would not be used until the product is ready. So if that takes say 3 months, you have a lot of time to figure out how to procure that packaging. This extra time you have is called float.
The float of an activity is the amount of time that that activity can be delayed without impacting the project duration. Using this logic, we can define the critical path as the path of the project that has no float.
Let us look at a simple example. Assume we have a project with estimated durations as shown in the diagram below.
The project has six tasks, A to F, with dependencies and durations shown in the diagram below.
To determine the floats of the activities and the critical path, there is a three step process:
1. Determine the Early starts and Early finishes using the forward pass. The early start is the earliest time an activity can begin. The early finish is the earliest time the activity can be finished.
2. Determine the Late starts and Late Finishes using the backward pass. The late start is the latest time an activity can begin. The late finish is the latest time an activity can end.
3. Calculate the float as the the difference between early start and late start.
Step 1: When we apply the first step to our example, we have:
The early start of Task A is 0 and late start is 10. Similarly, the early start and late start for the other activities are shown in the diagram.
Step 2: This step requires starting from the end (Task F) and moving backwards to the start. Based on the end time and the durations, calculate the late starts and the late finishes.
Notice that tasks C, D and E have different late starts and late finishes from their early starts and early finishes. This shows that these tasks have a float. Let’s examine task C in simple English: our analysis shows us that the earliest time task C can start is on the 10th day (after task A has been completed) but you can still start the task on the 20th day without impacting the entire project because as long as you have completed the task by the 25th day, the project would be on schedule.
Step 3: To determine the float of these activities, just calculate the difference between the early start and late start.
Using that formula, the float, or slack time can be shown on the diagram below:
The critical path of the project is the path with zero float. I have shown it with red in the network diagram in our example and this path is A – B – F.
I admit that this example was a simple one. What if you have a project with several activities? You can use project management software to create your network diagram and identify the critical path.
You might find a question on critical paths on the PMP exam; I would encourage you to practice as much as you can with many examples. Also, be aware that a project can have more than one critical path. Furthermore, changes to the schedule can change the critical path of the project.
One last thing about float: What if you estimate that a project would take you 2 weeks but the client gives you 2 months, so that the whole project has a 6 week float? This kind of float is called a project float.
Aside from the critical path method, the other tools and techniques you need to develop schedule include:
Resource Leveling: Optimizing resources based on their availability.
Schedule compression: Using schedule compression tools to reduce the duration of the project.
Scenario analysis: This involves analyzing the impact of different project scenarios (for instance, what happens if the lead developer resigns?) on the duration of the project. For complex scenarios with many variables, the best kind of analysis is a Monte Carlo Simulation.
The goal of the develop schedule process is to create a schedule baseline which would be approved and accepted by the project management team. This is a part of the project management plan. Other outputs of this process include bar charts, milestone charts, updated network diagrams and updates to the project documents.
The control schedule process is a monitoring and control process. This involves monitoring the status of the project in order to measure and report progress and manage changes that might occur to the schedule baseline.
The major inputs to this process are the project management plan (which includes the schedule and the schedule management plan) and the work performance information. As a project manager, you should compare the information available from the work done so far to the initial project management plan in order to determine if any change has occurred. The process of comparing actual values with planned values is called variance analysis. We will discuss variance analysis more in the next post, which is on Project Cost Management.
As part of the control schedule process, you might notice that the project is falling behind schedule and you need to intervene as the project manager. Some schedule compression techniques that you can apply include:
Crashing: This involves sacrificing cost in order to improve the project schedule. Examples of crashing can include approving overtime, hiring additional resources, etc. As a project manager, you need to ensure that additional cost/resources would shorten the project duration. You should also pay attention to other implications of crashing which may include increased risks of the project.
Fast Tracking: As an alternative to crashing, you can improve project schedule by fast tracking. This involves performing activities that are usually performed in sequence, in parallel. You should realize that fast tracking cannot be applied to activities that have mandatory dependencies because they must be done in sequence. You should also pay attention to the increased risk and changes to the critical path that can occur as a result of fast tracking.
The outputs of the control schedule process include work performance measurements (results from the variance analysis), change requests (changes to the scope, time or costs) and general updates to the project plan and supporting documents.
As usual, we have a diagram to summarize the inputs, tools and techniques and outputs of the six processes that are used in project time management.
Here are a few questions to test your understanding:
What is the critical path of a project?
What is the difference between float and slack?
Say the critical path of a project is A—C—E – G, if activity E is increased by 2 weeks, what is the impact on the project?
As a project manager, you can increase costs in order to improve the schedule. What is the name of this schedule compression technique?
If it takes 2 days to paint a wall, then it would take 8 days to finish up the painting. What kind of estimation is this?
Attempt the questions and drop your answers in the comments section. In the next post in the PMP Series, we will discuss Project Cost Management. Thank you for reading. See you soon!
References and further reading
A Guide to the Project Management Body of Knowledge: PMBOK Guide. Project Management Institute.