Well actually you will find most people in the hotel will actually sleep before dinner or just after...
Not exactly true. The ATM's (some of them) do give you the option of UD dollars or pesos but to get US dollars out you MUST have a local bank account. So while the option does technically exist it is not an option for anyone without a Cancun bank acount.
i pretty much was in the hotel till 9.30 usually every night then would head upto the party zone . we found a place late on with live cover bands so chilled there till it got busy over at the big bars and clubs. i wouldnt go down so early because why pay when its free in my hotel at that time