If you have already visited a particular studio the maximum amount of times allowed by your plan, or have an upcoming reservation for the studio that still falls within your current cycle and reaches your max, you will not be able to reserve another class at that studio until your cycle renews. The reserve button will be greyed out if you try to book another class. You will see a message that says you have already taken the maximum number of classes for the studio.
You can always double check your upcoming classes list and past class history to see what classes you have reserved or have taken. This can also help you determine if you have already booked max for a certain studio.
Keep in mind that missed classes and classes cancelled less than 12 hours before class time still count as one of your studio visits. Be sure to cancel any reservations you're not able to attend at least 12 hours in advance in order to avoid the loss of a class visit.
If you're unsure how many times you can visit a studio, check under 'Your current plan' in your Account Settings.