If the hardware doesn't have a clock that keeps track of the current time, the game could still re-seed based on the timing of player actions, because there's a certain amount of unpredictability there (at least, more than "seed with 0, only iterate on easily-controlled player actions"). It could do something like iterate the RNG every frame that the player doesn't move.

One of the reasons rare drops exists in RPGs is to arbitrarily extend playtime by hours.