Fastest I have seen was 8 days on DSCR which is some what common since its a lite doc program. Standard can go (2) ways ELA Express Loan Approval less than 12 days to close or going FHA, VA or Conventional with Rush appraisal and still under 18 days.
Biggest part is making sure the deal/loan is discussed in detail with banker, Processor, Realtor, Title company and appraiser cannot drag feet unless you use an AVM.