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The actual difference is only 8 hours... Europe vs America has this problem all the time
Furthermore, I can't just flip players like it's nothing. I'm 99% sure it's against Smogon's rules. Please just try to get your battle done as best as possible (Just to get you started, if the player who has -8 will play at eg. 9PM, the one with +8 will have to play at 1PM. That should be very doable in weekends...)