Pick up location on iPhone so time zone in app is correct

Pushover does not store timezones anywhere, all dates and times are stored as Unix timestamps and shown in the timezone of the device (including date/time format) when they are displayed.

If you are seeing messages with an incorrect date/time, this is probably being set by the sending application or from the Date header of the e-mail if using the E-mail Gateway.  There is an option on your dashboard for your e-mail alias settings to ignore the e-mail's date header if it is consistently wrong from a particular source.