The time zone for both server and php is UTC.
For example, I fly from KORD to KDEN and submit the PIREP, my pilot location and fleet location should be both updated to KDEN. However, if the arrival time in PIREP is ahead of the real time, like I made the flight on 10/30, but in PIREP it's 10/31, somehow the server won't recognize and update pilot's location correctly.