1. damo dont pay by time you pay by work completed.
2. My fault should have said this first. You have a detailed quote – how you asked a separate builder to do the same job? I would ask 3 to bid cost the job and then down select from that based on quote and warranty/time. This is normal commercial practice and ensures you get best price.
3. You agree the schedule up front by work completed. Dont agree a %. If the drive is laid and completed its done and you pay. Why?
This limits your risk in case they dont complete something. You dont pay and get someone else to do the work and pay them when they complete.
Its your responsibility to check the work done. You have a detailed quote. Standards – they should provide a warranty with their work. Ask to see it.
Final payment agreed in schedule after you identify the snagging and they complete the work. Job done full and final settlement payment.