After i submit bill how long do they have to respond, and if they don’t is it considered approved?
That depends on the terms of your contract. If there is no timeframe set in the contract or you have no contract, there is no law that requires them to respond. Also, if they don't respond there is no law that deems the ticket as accepted.
I hope you timely served your preliminary notice. Reach out to constrution attorneys if they don't pay.