Pre roll/Post roll   

In timecode applications it is important that the master and slaves all have sufficient timecode recorded before the first picture or sound event (pre-roll) as well as after the end of the project (post-roll). 
This is important for insuring that the devices have time to “lock” or maintain stable synchronization.  Although specific to the various devices used, a good rule of thumb is a minimum of 1 minute pre-roll and 45 seconds post-roll.