The 14900K(S) has an unlimited boost duration. It'll run those clocks until your cooler can't handle it anymore, they never give up on their own. Intel added this not that long ago to differentiate the xx900k from the xx700k.
Okay, but unless you have cooling with liquid nitrogen you cannot maintain 6.2 GHz for long due to thermals in practice, hence after a short sprint it will fall back to a much lower frequency.