I want to visit Longmen caves and then the Shaolin temple.

Yes, one day is ok to cover them both. Perhaps, you prefer to visit the Longmen Caves first and then temple. But you may have to stay overnight near Shaolin due to the limited time.

I remember the Kungfu shows are scheduled at 09:30, 10:30, 11:30, 14:00, 15:00 and 16:00. I went there in 2013. Maybe the time changes a little now. Go to check on your own.