Yeah, exactly. It'd have to be really exceptional cases. For example, exactly one game (Air Strike Patrol) has timed writes to certain video registers to create a shadow effect, but 2us is so minor I don't think it'd appreciably effect even that. Or, like, the SNES has an asynchronous multiplier/divider that returns invalid results while the computation is on-going, so if you optimized some code you might end up reading back garbage.

IIRC ZSNES actually had basically no timing; all instructions ran for effectively one cycle. ZSNES wasn't an accurate emulator, but it mostly worked for most games most of the time.