24 hours played time or 24 hours realtime from the moment you log in first?
Play time. I stretched my trial over a few weeks. There was even a timer somewhere letting me know how long I had left, probably on the same menu where you buy subscription time.
A F2P MMO generates more revenue than a failing P2P MMO is what I'm saying. You get a burst of new players that keep subscribers from quitting, and at least some potential revenue from people who don't want to subscribe, instead of 0. I really can't think of a case where an MMO went F2P when there were still very large numbers of people playing. In the instance of TOR, a few months before the F2P I saw a lot of people complaining their servers were ghost towns.
The next step after that is closing down the servers, if even F2P becomes unsustainable.
WoW and EVE have always had large numbers of people willing to pay the sub fee so they've never had to go F2P.
The publisher is going to switch revenue models as soon as they think a different one can generate more than their current one. The switch to F2P has more to do with the demographics of the players gained and retained: If your current subscribers are unlikely to spend much on average, and you don't anticipate drawing a lot of new players with disposable income, you don't switch unless you're desperate. Otherwise, switching can make sense after the initial population rush dies down, even if the service is maintainable on subscriptions alone. In any case, the length of time one retains a subscription model isn't a great measure of success: Everquest went for a long time before switching with little sign of it failing. The switch likely had more to do with the research and data generated by all the previous AAA games that had switched, like LotRO, followed by Sony realizing how much more money they could pull in. Asheron's Call has been around about as long as Everquest, but has never switched off a subscription model. Would you say AC is more successful than EQ?
Also, there isn't a good way ATITD could go F2P without becoming P2W, since most of the challenges have to do with how much material wealth and/or time one has.