Is five hrs enough time for benadryl to wear off before I take topamax?

I think you will be fine. Just be alert to symptoms of heat stroke. I think as long as you are not extremely active and you are in air conditioning, you will likely be fine. Stay well hydrated. If you have symptoms like increased body temp and not sweating, and also be aware of the possibility of additive CNS effects (e.g., drowsiness, dizziness, lightheadedness, confusion) and if you get symptoms like feeling very hot but not sweating and not urinating, be usre to call your Dr or go to UC/ER.