Iphone timestamp issue on US Local time

Hi,

Currently, i m working on iphone native app. i have tested the app. in IST(Indian Standard Time) local time and was working fine. But now we are facing issue like app. is not working properly in (US- PST)local time. whenever client do some tranctions it is going to the next day or previous day.  Date is automatically changed according to the time.

Anyone kindly help me how to test this issue in US time environment. Plz suggest some real time scenarios.

Thanks in advance

Chitra.C