I went twice last year with the kids, they charge by the hour, you get a wrist band which has the time recorded on it. you can check the time at a couple of digital stations.
think its 10 minutes changing time grace on top of the hour. thought it was slightly more then 9e, 12e maybe? maybe wrong on that.
great fun. well worth a visit as a novelty. fyi: theres no swimming there, wont need arm bands, water up to childs waist at most.