So, I played around with the /gamerule randomTickSpeed command in my single player world, setting it to random numbers just to see what it would do to crops and animal growth (numbers like 1000 or 500). I've set it back to the default (which is 3) but now my entire world is "lagging". That is, the sun jumps as if I'm on a laggy server, repeaters are slow, buttons are slow, tnt is slow, etc.
My world used to have the doDaylightCycle gamerule set false beforehand and I set it to true before playing around with the randomTickSpeed so I don't see how that could have affected it... I'm out of ideas.