If your account is automatically approved, your account will be ready for uploading within 15 minutes of you signing up! If your account is not automatically approved, it will be within at most 24 hours.
It will take a little bit longer for your domain name to actually work on the web though! New domain registrations and DNS transfers typically take 24-48 hours to work while the DNS propogates across the Internet. Your welcome email will give you all the inforamation you need to setup your site in the mean time.
