Any downfall to starting rehab after Pre-Possession?

[Jon Behlke]

My in-laws and I just got the signed pre-possession authorization on our first flip for a house that we close on in two weeks.  My father in law has been a landlord for over 40 years, but this is his first foray into flipping.  My brothers-in-law were excited to get started so they started working on the house already. 

My thought was that if we could get a substantial amount of work done in that two weeks, we'd be dodging some interest payments. 

But is there a downfall to this approach?