booking time issues if booking removed

Hi
Please see attached wb.
I have a mot booking wb that allows you to select a daste from the calender then book a test type in that day
and it will work out the next booking slot time.
the problem is that you have to book them in order as the next available time looks at the preivious one and if a booking is cancelled
it screws it all up.

My question is : is there a better way to allow a booking to be made at any time of the day and still allow/work out booking times befoe and after booking
i.e
if i book a 8am-9am mot it would know that i still have 3 hours of booking left, if my next booking was 10am-11.30am it would know that
i have 1 hour free 9-10 and half hour untill 12, also if the 8am-9am was canceled it would re configure to know that there was 2 hours free to book now.


Have i gone about this wrong? is there a better way to manage time slots in excel?


Any help would be apprieciated



http://www.ozgrid.com/forum/showthread.php?t=187379

Cheers

Peter