What's the best time of day for an upgrade?

Planning a trip to vegas in Sept. We have tried the $20 trick with mostly success several times. Some times it works and sometimes it doesn't. I was wondering, since i havn't booked airfare yet, are you most likely to get an upgrade if you check in the morning or check in later in the evening? Or is it just a matter of chance any time of day?

I don't know about best time of day, but it has always seemed like late afternoon to early evening when I got it.

I think it is also important in how you are dressed.

I have had fantastic luck getting upgrades when I show up in AC on a Monday after 8PM. No money involved, just from being a regular at the casinos and them having excess suites and ultra suites on a Monday night. I doubt it would work as well on a Friday nite.

I've gotten free upgrades at midnight, 10pm, 2pm and 10am. So, stick to just those times and you'll be good.