The estimate should include all work to be done for that contract. What specifically will be done. The price, type, and amount of the supplies. Any sub contractors and their part of the contract. e.g; plumbers, electricians etc.
It should also include any payment scheduals and at what point in the progress that is to be paid.
The starting date and projected completion date and any penalties for going past the date without reasonable cause for doing so. e.g; weather delays, componants that are not available or complete, such as cabinets or a specific type of appliance that has been backordered by the manufacturer for example.
Contracts are a very big grey spot in the construction business. They can include or not include many things. If your contractor has included a clause about 8 hour minimums then it is his right to do so. There is nothing that says he cant. Personally I would question him as to why it is included.
Pretty much you should have someone that understands the nuances of contracts look over the contract before you sign it.
If there is something in the contract that you do not understand then please be sure that you do understand it completely before you sign.
There is an excellant series by Dave Lupberger that I highly recommend you view before hiring a contractor. If you follow his advice you cant go wrong.
Please click here to view the series.
Please let me know if you have any other concerns. I will be happy to address them for you.