can I get a violation instead of flowing some tasks in a group to the next block of available time
 

I have a list of tasks organized under a group. The tasks are simply sequentially dependent, finish-to-start through the whole group of tasks. The tasks are individually complicated; Each has a significant amount of text in its notes field.

I want to have this group of tasks done outside of a resource's (a group of two people) normal working hours. I created an extra block of time which begins at the desired time and date. Then I set the group's "Start" to that time and date. The tasks in the group then fill into that block of time.

The duration of the scheduled block is arbitrary; I think the whole group of tasks is probably 3hrs of work, so I created that as the block. (Think: Now I can inform the people to plan to do this group of tasks from 3am to 6am on a sunday at a remote location.)

Here's the problem/question...

As the time and date approaches, we'll be tweaking the time efforts or adding/removing tasks. At first, I can make the block of schedule time perfectly match the duration of the group of tasks. But then with every change I make to the group of tasks...

If the total effort duration of the group is less than the block of time, OmniPlan dutifully pulls other tasks from normal working hours into this one-time block of work time. I don't want that; If the group of tasks is shorter than the block, then fine, don't fill the rest of the block with more tasks.

If the group no longer fits in the special block of work hours scheduled, OmniPlan dutifully pushes the tail-end tasks forward to the next available working hours.

The first case is a problem because it messes up future planning a little bit. But the second case is a big deal because it tells me we're trying to do too much in the window of time we want to schedule.

My hope...

A way to force absolute back-to-front scheduling of tasks in a group. Then with my group set to start when the scheduled block starts, a violation to be shown if the group of tasks does fit in the block.

Thoughts?

I haven't given any thought to how to handle situation 1, but situation 2 seems easy enough to handle. Put a milestone at the end of the chain of tasks in that "after hours" group. You could put a F-S dependency from the group to the milestone so you don't have to worry about individually connecting the tasks to the milestone. Set the end constraint on the milestone to the end of your window of time, and you'll get a violation if you try to put too much in that group.

That's an excellent and simple solution! Thanks.