The GeeFi usage model is based on daily passes, called GeePasses.
A day pass costs $9.99 USD, and gives you access for 24 hours to unlimited data. The 24 hours begins from the very moment you activate your daily pass. So if you begin using a daily pass at 4:47 PM on Wednesday, the pass will expire 4:47 PM on Thursday.
This 24 hour period, is regardless of time zones you might be crossing during your travels.