MSS will book you into the first available time based on your criteria.  If you are flexible and search a time window from 6-10, MSS will offer you the first available time for each location in your desired city.  If you need a specific time, for example 3:00 pm, select 3:00 in BOTH the earliest start time AND latest start time.  This will only show results for 3:00.  If the spaces are not available, then expand the search criteria (3-4, 3-5, etc...