how to build a time line :
-estimate time needed for each task
-multiply by 2 each duration if common people are implied
-multiply by 3 or 4 each duration for task involving managers
-asume u'll be 1 or 2 month late whatever, because just letting people know the schedule will enhance delai.
Dear project team member,
Thanks for submitting us your finish date.
We'll let you know what your tasks are around one week before that deadline.
Regards,
Project management