The registrations open at complete random hours so there's no set time as to when they open. Ye' just got to have a little bit of luck on yer side. As said by madam Whisper, try checkin' here on the forums once every hour or so to see if they're open as when they do open, they remain open for 2 hours before closin' again. T'is the most I can give.
Lockin' this thread for now.