Hello,
At this time there is not a way to see all employees availability at the same time. You are able to click on each employee availability through the employee tab. Also when you are creating a schedule the employees availability for that day of the week is shown on the top left corner of the pop up box you use to put a shift in. Your suggestion has been taken into consideration for a future update to Zip Schedules.
If you are dealing with multiple students with varying schedules, it makes hard to schedule at a glance to see if they are available or not.