Closing date time frame

I am new here, but I have heard from some land flippers that it takes 2 weeks to close, one of the perks of selling to an investor right? There’s no lender, etc. In a regular real estate home transaction (with a realtor and lender, it is 30 days.) I understand there are alot of factors there, but just saying that for comparison.
So do you go with 30 days in the contract and just extend it? And is the seller always aware that the contract is being sold? Thanks!

@dca I always make sellers aware that I’m wholesaling the property. I usually structure it as a double closing, so in the HUD/Settlement Statement and Warranty Deed, I’m still the buyer on file. I recommend getting it under contract for a minimum of 60 days. Ideally 90-120 days to give you enough time to find a buyer to re-sell the property to. A cash closing can happen as quickly as 1 week (depending on the bandwith of your escrow officer). Many times buyers want to order a Survey, which can push closing back a few weeks.