If it was simple hernia surgery, and he has no complications from the surgery, he should be fine. He will be a bit sore at first, but after a week or so, fine. You say he is your Dad--if you have kids, don't let him lift them up. Any lifting, weight bearing stuff is hard on a hernia-recovery person for a good 6-8 week period to insure a total recovery. But for just walking around, riding rides, etc. he should be fine.
Tell your Dad's surgeon what you have planned when he comes out to talk to you post-surgery. The surgeon will tell you if your Dad's specific case requires any restrictions.