Are you planning to make the building energy efficient in your restoration work ... what other updates will be required by regulation / legislation?

Compounding the problem, Congress has not given the Treasury Department time to say how the law is going to be enforced and issue Regulations (a process that can take months).

Still, a significant number of my clients would be affected.I wonder about the mechanism to enforce such rule.

With that said, if waiting until 2018 will cost you $5000 in holding, taxes, etc... paying $500 now to expedite an appraisal would make a lot of sense (assuming this works and there can be an enforceable contract put in place to be certain things close as needed).Just throwing ideas out there.

Inform him that you plan to have him sign a lease (I am guessing you don't have one in place since he is a friend; if you do you need to revise and/or enforce it). 

Unless you don't have the reserves to pay the mortgage on the 1st unless you have the tenant rent check, then it really doesn't matter.....you re still getting paid at the same time every month.....If you were running 15 properties and were trying to work with 10 different dates, sure it would be a huge PITA....but if you are doing just a couple, I don't see the big dealI would set his payment on the 10th...late past the 13th...and be strict as hell....NO EXCEPTIONS....ALWAYS enforce the late fee....no BS stories....The big issue is the upcoming rent increase......let him know it's coming...... don't budge on it happening.......and the issue may move itself out anyway.....

And these are more strictly enforced than for houses. 

Yes, the contract doesn't have to be in writing, but its very difficult to enforce anything unless its in writing. 

It’s rare, but a bank can enforce this clause.

Has the changes in legislation in re: to hotel taxes or allowable days a home can be rented per month effected your business?