I just did the same thing this week: had to call about delays that I would be arriving around 330-400 in the morning. They told me they had an automatic cutoff time for no shows at 200 am at that property. They were able to mark my account that I would be arriving late and everything worked out fine.

I would assume that each property has a different automatic no show time.

One thing to note is that while I was checking out, they had a problem with marking my room as used and needing to be cleaned.