I was playing Terraria and my game has sped up and i'm not sure how to change it back

Check to see if you have lag, as your game might just be trying to catch up to the server. Try restarting your server, and if that doesn't work, then you could try making a new server. Also, you might have accidentally clicked on an Enchanted Sundial. If that's the case, waiting for 1-2 full Terraria days will stop it.

So to recap in simple steps:

1. Check to see if there is lag.
2. Wait 1-2 Terraria Days (With a player joined on the server)
3. Shutdown and Restart your Server.
4. Try a new server. (You could port your old server world to your new one if there is a way to do that.)

My current thought would be that the game has somehow bypassed the built in VSync and is in fact sped up, due to the fact that some of the games features are locked to fps and as such, speed up and do wacky things when above that limit.

I had a similar thing happen to me. I had an online multiplayer world and I closed my laptop without saving and exiting. When I came back around 2 hours later, re-opened my laptop (which auto-connected to the wifi) that's when the world sped up. It has returned to normal now, but I had around 20 minutes of gameplay where it was jumping in game hours every 5 or so seconds.

My theory is, as it was still technically online the game was keeping track of the real world time that had passed, and attempting to catch up. This ended up putting the world into a glitchy overdrive to do so. Either way, just playing the game for a short while was able to fix the problem.

If you experience this on any world, check your settings. If you have Frame Skip set to on, you may want to set it to subtle or off. If you want more details on how this setting works, click here.