How to run cron only as per `CST` time zone inspite of being saved in different timezone

I have simple question, it might look simpler than what you folks accepted here in stack overflow. My question is:

I have to run all my cron job as per CST time zone. for e.g. I saved an event whose start_time is saved from IST timezone or may be another timezone let's say 2015-09-09 06:06pm but actually it saved in UTC timezone on aws server, so how do I check on server that event start time is under 15 minutes as per CST time zone.

Actullay I want to run a cron when time in CST timezone is equal to 2015-09-09 05:51pm. Please let me know how to do this in ruby on rails.