It'll be interesting to see how the timing is enforced. Can you just set up your own NTP server to fool your phone into thinking it's really the future (and not just you adjusting your phone's clock manually). Will Google run a clock that you have to get a timestamp from (would it be easy to setup your own MITM proxy to get around this?). If the time somehow jumped backwards, would you lose the ability to install apps? Can google remotely disable this after it's already enabled (I think yes)?

It requires an internet connection to adjust the toggle.