You can now gray out the booked time slots when the calendar loads. This was a highly requested feature and is now available as a setting. You can access it via the
Settings
tab > Storefront
section. 
When this setting is enabled, your calendar will automatically gray out any dates that no longer have availability. This will make the calendar a little slower to load but should make it a better experience for your customers.
We're looking for feedback for how this works on your store. If you have feedback, please leave it here.