From this 6/6/12 Positive Rate
If the issue is an assignment outside of requisite timelines, please politely raise the question with CRS. Additionally, ALPA requests that you obtain relevant data from CRS and then contact Contract Enforcement. This might arise if a pilot is assigned a Base Airport Standby. The duty period begins at showtime for the standby and the "duty period in which the pilot is not assigned a trip shall not exceed 5 hours." CBA 12.B.3.a. If a pilot is assigned a trip after the base airport standby duty period, the pilot is not required to accept the assignment. Please keep in mind that if CRS disagrees with your contention, this is a “Fly now/Grieve later” situation.
Did the Union seriously put this out?