Hi Billy,
Yes, if your site doesn't currently meet the requirement you can still
use the sandbox, but we won't be able to approve your application to
launch your implementation live. If you are a growing site, it still
may be a good idea to build your implementation and then you will be
ready to "flip the switch" when you hit the page view requirement.
More on the sandbox here:
http://code.google.com/apis/adsense/developer/adsense_api_sandbox.html
Cheers,
Ryan
Google AdSense API