Right from the day one, I started facing this strange bug on phone calendar. Any alert that I put in the calendar would go off 3:30 hrs before its scheduled time. I tried to find what was going on and I would some issues with Automatic Network Time from Airtel Network.
When your date and time settings are set to "Automatic" the time zone goofs up at times and because of that the alert goes off at a wrong time. The resolution to this problem is to manually set the time and time zone to IST.
After that I have not seen the problem at all.