While we model our world as continuous quantities, doesn't QM give the necessary leeway here by imposing limits on measurement? If you computed fields as grids with grid points that are half a plank length apart, then added some "quantum noise" (just good pseudorandom noise in the right distribution), could we tell?

For things like light frequencies I believe we are not even sure if they are truly unquantized, so they might be discretely computable for all we know

Time is the tricky one. But if you get away from computing the whole universe and just try to compute the viewpoint of one observer that might be quite solvable