Technically, there's no way that it wouldn't have an effect on time. Even a year later there'd be SOME difference that it'd cause, and the same can even be said for a minute later. However, talking to a villager in 600AD would have an impact on 1000AD, but actually changing the world each time you do something in the past is impossible for a SNES game. That example isn't exactly similar, becuase, for all we know, even in the simplified laws of time-change (where talking to people and doing things in the past has little or no effect in the present/future), something could've happened to the mainland... Hell, there might even be a whole nother Chrono Trigger, where Crono and co. do similar actions as in Chrono Trigger, but with Porre militarized, and w/e differences the time crashed caused.