I have a problem with a new assignment. Have made a booking tool for a sportscentre. The sportcentre has 3 rooms that they can lease. A small room for dancing, great room for basketbal, volleyball,... and an onther little room for school.

My assignment is I have to divide the rooms in 15 minutes. for example
8:00 - 8:15
8:15 - 8:30
...

There is one problem I want the people the get a restriction of 60 minutes. After 60 minutes they can hire more hours, but first they has to hire 60 minutes.

I tried something like this time unit 15 minutes and min limit at 60 min. When I use this adjustment I get an error:"select starttime, select endtime.

I hope can someone help me with this problem.