If reality were a simulation then there would be one absolute hidden variable behind all phenomena, the clock-pulse of the simulating 'engine'. But this would only be true if the physical reality were primary and the subjects, or observers, the experiencers, or subject-windows were subprocesses as in any kind of up to the minute materialism - the synchronisation of which would be intractable The simulation would thus more likely be arranged in an idealist mode, that is, with weakly parallel processes for each observer, and the 'external' reality a sort of common nexus between them shading into fuzziness where required. But again, as soon as you have made this move the logical pull towards the idea of a simulation vanishes entirely.