PFrog,

From "When Scheduling Calls"

Required Schedule Checks
A reserve pilot must check his schedule and acknowledge a rotation,
short-call period, or rest period under two circumstances:
1. Last Non-fl y Day: On his last non-fl y day prior to an on-call day,
a reserve pilot must check his schedule between 1500 and 0200
base time. He may be required to report for a rotation or start short
call as early as 0500 base time or start rest as early as 0001 base
time, provided Crew Scheduling has placed the duty or rest on his
schedule prior to 1500,. If is no duty on his schedule prior to 1500,
then he simply becomes a long-call pilot at 0001"