Yes, you can do a cost segregation study in a year after the property is placed into service.However, you will need to file a form 3115 which basically says you screwed up the depreciation in the past and as a result recalculating the depreciation.

I am also an investor that does flips, has rentals, lend my own money, has owned STR and have been a member of the local REIA for over 10 years, So hopefully my experience and network of other investors could prove useful in evaluating the potential of the property and possibly attract a partner if you need. 

Does anybody know if my father can prove his income to a lender when I try applying for an FHA loan instead of my income?

Vacation homes take some planning, I personally think shooting for break even profit/loss with a vacation home is a good tax strategy but if it is a cash cow I would gladly just pay the tax as you still come out significantly ahead and if you have one I probably wouldn't bother with a cost seg study unless you are getting extremely high rents.

Study the market.

Can they prove how long it takes to rent a vacant property?

I've been trying to find possible partners but it's proving difficult.

Can they prove how long it takes to rent a vacant property?

However, verbal agreements can be legally binding in court if there is enough evidence to prove the agreement's existence and terms. 

Almost all builders can do the development work for you, but that's a unknown cost and nobody can give you an accurate quote without studying the site.