closing on home Nov 15, house note due Nov 15

well technically its due the first with a "past due" of the 15th

Pay it.

I thought you have up to 30 days before it affects your credit?

if your closing a refinance ask your LO what day they have the payoff good for. i would pay the late fee. your just paying a bunch of interest anyway.

Call and ask for the late charge to be waived if you get one. Doesn't affect credit unless it goes over 30 days. You can't get it waived until the late charge shows up. So if you have a 15 day grace period you actually have until the 16th pay. The 16th is on a Saturday so call that Monday and request for it to be waived.

Why would there be interest due on day 1?

Pay it. You will still get that money back at closing. Plus you run the risk of late fees if the closing gets pushed back. And the payoff amount could change on the 16th due to a late fee which will cause additional headaches.

$500 interest in that $750 payment is still going to occur whether you pay it or not. It's not like you are throwing away that $500...if you don't pay it then your payoff balance is $750 higher than if you paid it.