Schedule

I set up my schedule to offer an hour lesson every other hour.  This way I am assured that I have an hour between each lesson to prepare.  However, on my profile, it looks like students may only sign up for a half-hour lesson.

Are the times listed as when the students may begin a lesson?  Or do they indicate the available length of the lesson?  Do I need to set my schedule up for 90 minute intervals to offer 60 minute lessons?