Not only regtest could activate bip16 earlier than 1333238400 (aka Apr 1 2012), but also altchains rebasing on top of bitcoin core could activate it from the beginning of time (aka time 0, long before 1970's epoch and height=0 because bip16 was faulty in using time instead of height, but it is fine to "abuse" uint32_t for 2 purposes here).
Depencies:
- [ ] BIP90: Make buried deployments slightly more easily extensible #11426