Nurr, as it's been said time and again, registration opens only at random. The staff don't know when it's open, and even Razmirz (the one who set it to open/close at random) doesn't know the next time it'll open. (xD)
However, it will open daily, so there's no "prophesying" to it, I'm afraid, lol. The trick is just to come online every hour or two to check it (minus when you're sleeping). You will find it open. I remember catching it open at least 5 times this past week, and it stays open for a good hour or two before closing again.
@FoxPhilosopher; You mentioned "sharing accounts," or passing off accounts to other users until they can find registration open.
I'll have you know, though, this is a very bad idea.
Foremostly, it's warned against in the rules. "Your account, your responsibility." By opening someone else's account, you are instantly linking your IP addresses, and therefore if one of you acts up and gets banned from the game, then so does the other. Even if you only opened it once, you're still linked.
Never share, give away, or accept accounts that you have not made on your own.
Have patience and wait for registration to open, this way you can be assured that you'll have the opportunity to play FH without worry for as long as you like.
This sort of question has been asked before, though, so I lockies this one.