Need dates/hours to be unavailable as soon as they are booked

When someone registers for a session and chooses a date how do I get it to cross a line through the date and time so no one else can choose that time and date.  For example on this form Dec. 4, 2015 Time: 6:30 at the bottom.  Someone already purchased this session time, but it did not show it as already booked.

For that you can use some widgets instead of a radio-button field. One of them is appointment slots:

http://widgets.jotform.com/widget/appointment_slots 

http://widgets.jotform.com/widget/gift_registry 

You can test them here:

https://form.jotform.com/53184524896971? 

Let us know if we can assist you further.