Andy,
You don't and neither does anyone else. Project uses a defined
scheduling engine. That is, all tasks have a start, duration and finish
expressed in real time (i.e. no TBDs).
Just an observation but every scheduled project I've have ever worked
has a real end date. Most of the time that date is pretty "hard" (e.g.
contract requirement). Even though you may not know when a particular
project will start (and hence finish), the whole plan can be shifted
when the scheduling requirements are finalized.
John
Project MVP
