You could use timer boundary event attached to the user task node. This (attaching boundary events on task) is supported from version 5.3 and as I can see you are on 5.2. So either you move up to 5.3 or you could put your user task in embedded subprocess on which you can attach boundary events.
thanx a lot for ur help..can u pls help me out as to how to attach the boundary event on the embedded sub-process??