Standbys with the company I work for last either 8h, 7h, 6h or 2.5h
Start time anywhere from 0300 to 2130
either Home Standby or Airport Standby
if you are called out from Home Standby you are required to check-in within 90 mins
from Airport Standby you are on immediate call out
The standby start time will reflect your current run in the fixed roster pattern, ie early start if on earlies or a later start if on lates