When do I have the Contractor give an estimate on Repairs?

[Parker Shoaf]

After evaluating deals and having a shortlist of 3-5 that could potentially work.  What is the process like or when is it appropriate to have a general contractor go out and give me the cost of the Rehab?  I want to respect their time and not have them go to a ton of places for no reason.  I hear answers like during the option period, but that's after it's already under contract.  Other than a generalized rehab number from my own estimates how does the actual General contractor and more precise quotes all come into play?  Looking for like a step by step blueprint as I feel like I'm missing a part in my mind. Thank you!