Avoid churning the schedule by deferring rescheduling until the cumulative slippage is large.


It's difficult to know how long a project should take, and even more difficult to recover when one guesses wrong.  Keep a track of how far from the scheduled times the critical path tasks are being completed.  When this amount becomes too large for comfort (o.p. suggested ‘ludicrously large’), then re-work the schedule.  Before that point, you keep track of a ‘delusion index’ that tells how far off the schedule you are. 


Take No Small Slips


The comfort point should balance the need for accurate schedules against the need to avoid excessive visits to re-work the schedule.  This pattern can be applied both to tight and lax schedules.