When setting up your Showcase, there's a section on Availability. Set the days of the week and the times of day that you want to keep open for clients and prospects to choose from.
In addition to that, you can connect your calendar too! This allows Simply.Coach to ensure that you're never double-booked through the Showcase page, as the only slots that will be open to clients are those that are free on the calendar you have integrated and fall within the timings you set here.
Related: Connect Your Calendar