What is a reasonable length of time to ask a builder to deliver a quote?

[FlowersandFunk]

In the new year we are going to ask a few local builders to quote for an extension/renovation job on our house.
We have already had a couple of quotes and they took forever to get back to us.
Now we are almost at the new year I would like to decide on a firm and get a start date booked in. So once the new builders have been to view our house and have the drawings they need, is it reasonable to ask for the quote to be submitted in two weeks time?

I was a Construction manager before i started my own firm but we had a massive team of sales and pre-construction team working on getting new contracts in.
As a new firm on the scene i do almost all the managing and pricing, visits, contracts and estimating. If i had to pay a professional estimator it would cost me 270£ per each bid we do. We get about 28% of the jobs we bid sometimes the clients are only worried about the price and we have had times when i have seen jobs left half way through because the cowboy builder under priced the job and left half way through it. So now after a year of running a successful firm and happy clientele we get a lot of return business so really chasing jobs is not our problem anymore however i do chase up an estimate and if a client tells me he is getting more than 3 builders to look at one job i no longer bid for it knowing full well that its a waste of my time sitting and doing a quote for someone who most likely is not even sure he wants to do the job. I do tell them the time they will get the quote and i will book a phone call to discuss it with them if they are not available that means they are not serious. I don't care if they think i am desperate for me its like a screening process which means i don't waste time and energy on something that is pointless i choose to pay attention to my clients whom i currently have and do not ignore their needs.
Beware of clients who change builders often there is always a reason in my opinion. Just wish someone had shared this with me earlier.