I mean, have some sympathy for the dancers/actors, to do the routine every 20 minutes, everyday is bloody hard. That is a lot to ask of them. Additionally, having set times for the shows allows all guests to know exactly when the show will be. Because every 20 minutes could be that when you turn up, you just missed it perhaps.
I visited last week and waited 15 minutes before giving up, I didn't know whether I had just missed one or not, and I wasn't keen on just waiting around. I would have preferred to know an exact time when the routine was going to start.