Upgraded to Web Developer Account from Hacker Account after 2 weeks how does billing work in this instance?

Hi, just upgraded my hacker account to a web developer account after 2 weeks (impressed with service). How will the billing work in this case ? Ive had no new invoice email etc so far and account is clearly upgraded as It says upto 3 web apps available etc.

Thanks for upgrading! We'll start charging you the new price as of your next billing date -- think of the two weeks of the web dev plan at the Hacker price as a thank you from us :-)

Thanks Giles ! Another great example why Im impressed with the service, a prompt response to my query and a great billing policy. Thanks again ! :)