This is a topic that comes up often, the real answer is that it depends. In short minimum is around 4 business days and most is around 10 business days. Both of these examples are specific to purchasing a normal residential property that you plan to occupy. Its rare For 3 business days to be enough you need to have all of your documents with your lender ready to submit once the offer is accepted and a lender that isn’t currently backed up with applications. Also an appraiser that has no backlog. In my opinion 3 days isn’t normally enough for majority of the situations. Inspections can usually be done in 1-2 days if the market isn’t crazy.
I typically recommend 5-7 business days as a minimum. This gives time for your lender to request and any additional documents or in case there is some back and forth regarding the approval. It also gives time for an appraisal to happen without a rush charge. Again with 5-7 days you can book an inspection after the mortgage is approved so that your not spending money on an inspection if your mortgage doesn’t get approved.
In a buyers market you could get 10 business days and you might need them if you own a business or have very complicated financials and don’t have all your documents at your mortgage provider. Now I always recommend having all of your ducks in a row before writing an offer however sometimes your not looking for a home and the perfect one pops up and you are caught off guard.
Regardless of your situation its always best to ask for more time then you think you need. Why? Because asking the seller for more time significantly reduces your negotiation power. If there are some issues with the inspection or you realize you need to make a change to the contract the sellers may want you to give up some of your conditions in order to get more time.
For commercial and investments these times can be significantly longer and I suggest taking those on a case by case basis.