Checking in a day late
 

I booked a room at a non-refundable rate and mistakenly booked an extra night on the front end (forgot to account for an overnight flight). If I let the hotel know I'm going to be a day late checking in, will that be a problem? I just don't want to have the rest of the stay canceled as a no-show.

Get in touch with the hotel. They might let you adjust the dates for no charge.

I believe it's a general rule of thumb that you have to show up before the hotel's regular check-out time the next morning. But of course you can call the hotel or have HGP put a note on your reservation as well and there shouldn't be any problem.

Ummm, no. There is no such rule.

If you do nothing then the hotel will mark you as a no show and cancel the rest of your reservation. The time at which a hotel does this varies. The closer you get to midnight the more likely it is to be cancelled.

If you do contact the hotel, they may change your reservation accordingly, or at worst simply 'prebook' the first night. The benefit to the latter is that your room will be ready whatever time you arrive at the hotel, prior to the original check in time on day two.

We prebook hotel nights to guarantee check in prior to check in time, especially after a long flight. We also contact the hotel via phone to confirm. Front desk may overlook notes left by Hyatt or a Private Line agent, so we aim to avoid this.

Although I have not done this with a prepaid reservation, I have never had problems contacting a hotel concerning travel delays and doing a shorter stay.

I'd just call GP and have them work with the hotel. As a diamond they'd probably just trim off the first night.

I've checked into hotels early mornings before with a booking starting the previous day so midnight is certainly not a problem

But it can be if the hotel is fully booked.... so the smart thing is to let them know. Or even better here ask about cancelling the first night, the hotel might indulge you if you have a multiple night stay.

Definitely contact the hotel and tell them your expected arrival time. They might let you push back the dates if you need to. If your check out date will not change, you could A) keep the reservation as is if you want to check in early, or B) possibly have the value of the first night room charge credited toward incidental spend if you do not need a guaranteed early check in.