In some cases, work for a customer may extend beyond the hours defined in a Block of Time Contract. In this case, the system will warn the user when trying to add a Charge for a Contract that has reached its limit, and then you may wish to set a special hourly-rate for the hours used OVER the amount allowed in the contract.
A good way to do this is to create a Labor Item that has a fixed hourly-rate, (rather than taken from the employee rate), that will be used to Charge overtime hours. For example, add an "Exceeded Hourly Rate" Item and instruct technicians to use it when they receive an alert/warning message that the Block is over-used, and the special rate will be taken for this from what was set for the overtime Item. You can define several Items with rates per type of Contract (e.g. "100 hour block exceeded rate" etc.).
Note that CommitCRM does not automatically bill customers, since it can vary from customer to customer, and from case to case. You can manually set the Charge as ‘Billable’ in this case.