I turned a survival world my friend and I played on into a realm, and now it's somehow stuck on always day.  The daylight cycle switch is off, but cheats are still off. No one turned it on, and we still get new achievements, so I don't know how it turned off when it wasn't off before.

The only way I can think of to turn the daylight cycle back on is to enable cheats, but with this being our full survival world, I really don't want to enable cheats because then we can't get all the achievements anymore.

We still get new achievements, which is how I'm certain that cheats were never enabled. I don't know how or when the daylight cycle switched off, and I have no idea how to fix it!