Future-rest

Future rest is a term most notably used in the Army for any amount of time consumed by an individual to rest, relax or sleep prior to an event that will cause you to tire i.e work details, guard or missions. Similar to a nap, it differs only in that future-rest is taken when previous knowledge of a future work related event is known.

Pvt.Joe: Hey, you want to go use the computers?
Spc.John: Nah, I'm going to get some future-rest before we have to fill some sandbags.