These are Android phones? And you can't manually change the time in the settings? Madness.
Idea #1: Seriously, change it in the settings.
Idea #2: Maybe you could put an activated SIM card in each one for just long enough to set the time from the local phone network.
Idea #3: as long as all the phones times are the same, and they are all wrong by the same amount, you could just let them record the date and time incorrectly and then after you aggregate your data, open the CSV in Excel and transform the dates with an Excel formula, adding or subtracting the appropriate number of hours.
~Neil