booking time slots

Hi

Not sure if this can be done.

At the moment the attached booking sheet adds the allocated hours to complete the mot in column b and adds the next available time slot in the cell below.
this has to be done in order so that it knows the next time.
Is there a way to allow me to book one in at say 9.00am to 9.55 and then the next booking taken might be for 11.30 am then the one after that at 10.00 (or any time) and still be able to work out that between 9.55 and 11.30 i can still book in a 1.35 hour job?

Also if a booking is cancelled it would just re set the time available and if the booking wants moving the booking data could be easily transfered??

Does anybody know of an example time booking code that i might be able to adapt for my wb?
I still need to select the type of test which has a time attached to it, but i would like to beable
to add the booking to any available time slot, or remove a booking making that time slot available again.

in theory we could have 12 five minute re test booking in one hour or a 55 min full test then a 5 min re test
or any number of different bookings .
at the moment each booking has to be in order as the times look at the on before and add up the next start time
but this all falls down if a booking is removed or a booking is wanted at 11am and theres nothing booked before it.

The calender booking works well its just allocating time slots thats the pain

If some kind guru could assist me in this i would be grateful