Similar policy, similar ambiguities, similar disinterested hotel management, and similar outcome. Wonder how many innocent customers are victimized by these two expensive properties? I have no problem with merging the threads.

First I thought the deadline would be Sat. 23:59, but the word 'until' made me realise that it should be Fri. 23:59 local time. If they had used 'by' then it would have been Sat. 23:59.

I think it's standardized Marriott phrasing, this is from a dummy booking at a CY:

This is for an advance purchase rate, and you have 24 hours to cancel the ressie. So naturally I would expect I should be ok if I cancel this ressie before 23:59 today at hotel local time.

Twenty different people could read the language and end up with 20 different interpretations. That's the problem with ambiguous language. Your interpretation is possible, but most folks I've talked to don't read it that way. As noted in the original post, the overriding rule of the property is that you must cancel three days in advance. Using your interpretation would necessitate canceling four days in advance. (Must cancel Friday for a Tuesday reservation = 4 days.)

When I had something like "You may cancel your reservation for no charge until Wednesday July 9 (1 day[s] before arrival)" and canceled around 2pm July 9 I got some kind of warning message that I may be charged the late cancellation penalty. When I then consulted customer service, the agent told me it's free to cancel until midnight hotel time on the date mentioned.

I then went ahead and canceled and was never charged anything. But then again, next agent might have answered something else entirely and different (or even same) property might interpret the policy any way they want (or is the possible charge for late cancel handled automatically somehow?)

I had a reservation that also offered no time, and said 1 day before arrival. I too wasn't sure what that meant so called the Platinum desk. The rep stated that if no time is shown it means 11:59pm Hotel time 1 day prior. Not 100% sure I'd be willing to do that online even with her assuring me. So I had her cancel me on the phone (which she clearly stated would be without charge). I'd much prefer to see a time stated, although it does provide confidence that a Platinum Rep provided this info.

Well this is what I got as an answer too - 11:59pm hotel time.

I have cancelled reservations with these terms late evening (though not quite 11:59) the day before online and never had an issue with being charged a fee. I do typically get the pop up warning box about fees but as long as it is the day before, never been a problem.

--Jon