Here's the typical fare rules (K class) on standby:

12. ....STANDBY PERMITTED FOR EARLIER/LATER SAME DAY FLIGHTS OTHERWISE STANDBY NOT PERMITTED. ....NOTE - 1. STANDBY A/ STANDBY FOR CO-TERMINALS OR MULTI-CITY AIRPORTS WILL BE CONSIDERED THE SAME POINT. STANDBY FROM A CO-TERMINAL IS ONLY PERMITTED ON THE CONTINUING/RETURN SECTOR WITH ANY ADDITIONAL COLLECTION IF APPLICABLE. CO-TERMINAL STANDBY ON THE OUTBOUND SECTOR IS NOT PERMITTED.