Hello John,
Our plugin does not currently have the capability to mark events or time slots as booked. It may be possible with some customization or a third party plugin, but that’s not really something we can assist you with.
I don’t quite see how the calendar is integrated into your order form on the link you provided. It may be possible to use our plugin, but again it will likely require some customization. What I recommend is that you download our free Events Calendar plugin and experiment with using that. If you decide that will work for you, you can then consider upgrading to Pro, which gives you added functionality, support, and automatic updates.
I hope I answered your questions. Let me know if I can clarify further.
Cheers,
Leah