Thanks for the quick response and info. I'm definitely trying at the right time - I saw that page displaying '1 minute' and then '23 hours 59 minutes' after refreshing, plus the sign-up page showed 'We're sorry, but the daily signup limit has been exceeded...' a few seconds before I refreshed again to get the sign-up page.
[EDIT:] I seem to have made it in now - the signup form is hanging around for a while longer tonight