Thanks for the reply,
I did attempt to start but my knowledge in php is some what lacking!
I was thinking the user could have the option to pay either now or at a later stage when choosing the time slots much like this:
When the user ops to pay now they will be taken to a checkout screen that calculates the total for charge per hour/s etc (maybe the charge could be set via an admin screen or a config file??)
Also do you think it would be possible to have the system automatically approve pre paid time slots and change the status color to an approved/paid color? Also to have the option enable/disable this feature as all users are of course not going to want / need it as you said many have the own internal billing system.
One more thing i think would be a good idea if to add the title tags to the submit buttons to make them a little more descriptive.
Once again thankyou and i am pretty sure when enough people no about this software it will be as popular if not more so then many well known open source shopping carts or forums!
If there is anything i can do to help let me know