Hi Asim,
please check and follow the instructions which are provided in SAP Note: "1912165 - SYB: Discontinuous execution of scheduled jobs" if you are running Sybase ASE 15.7.0.110 or higher.
If run an ASE version lower than 15.7.0.110 try the following workaround:
1. Delete the existing reoccurring job
2. Schedule a new reoccuring job (e.g. every 1 hour) which starts at the next day 00:00: o'clock
3. Schedule a new reoccuring job (e.g. every 1 hour) which starts at the current day next full hour and ends current day at 23:59 o'clock.
Best regards
Christoph