Well, I would definitely change your password now, so whoever it was can't log back in. Or.... Wait, did they actually HACK your account, as in you can't log back in (they changed your password)???
...well, he posted this...
I really doubt anyone's hacking you. Your timezone mught be off from the PB one,or there may just be a problem with the clock. Change your password if it makes you feel better, but I don't think anyone would really want to hack a random member of a Pokemon forum :/
The only thing that you can do is change your password, also as long as they aren't posting, sending you PM's, or getting you in trouble with the Mods I wouldn't worry too much. Like it has been said many times, change your password.