I agree with wilful - signing a contract with all the numbers and what is supposed to be included, including deadlines - firm ones - is pretty final unless the parties for some reason want to renegotiate but probably with some consequences - which should also be described in the contract.
This is especially true of a construction to permanent loan on a new home. There are lots of if's - construction cost can go up (or down), deadlines may not be met with supply chain issues - one has to take what's in the contract or both parties have to renegotiate all or part of the contract.
In real estate, one has to always be aware that market rate could fall - but on the other hand, hopefully you locked in a better rate than what is currently available.
It's Always Something . . . . Roseanna Roseannadanna