This topic explains one way to save time when scheduling a project, and describes a trap that project managers (particularly new project managers) fall into . . .
There's a law that comes into play when creating a project schedule that I call the Law of Diminishing Foresight. It says that the farther out you schedule, the less you know about what really is going to be happening in a project. Put another way, the tasks that you schedule 18 months out are far less likely to actually happen than the tasks you're scheduling for next month.
You're creating the initial project plan, laying out the tasks. The first few months may be crystal clear to you. You know exactly what needs to be done, who will do it, and how long it will take. As you move on the the middle of the project, you start to make some assumptions. First, your plan so far will come to fruition. Second, the project requirements won't change much. Third, you'll know what resources will be available. Of course, the more time goes by, the more risky these assumptons become.
By the time you're scheduling the end of the project, you have a strong sense that the tasks you're scheduling will need to be changed.
Still, I see people create schedules where the end of the schedule has as much detail as the beginning of the schedule. The project manager obviously put a lot of work into breaking down the project into tasks, durations, and assignments as far as 18-24 months in the future.
In my opinion, this is largely wasted work. Requirements change. People come and go. "Stuff" happens.
Think of a project plan like a photograph or a painting. The subject in the foreground is sharp an in focus, and the details of the background are blurry, and not entirely painted in. As the project moves forward, you can paint in the details, but you'll be able to do so with much better accuracy, because you have the benefit of experience and a closer vantagepoint.