The short version: If your monitor has a 60hz refresh rate, you're fine. If your monitor has any other refresh rate, turn off VSync, and you should be fine.

The long version: Unity, the engine Ori is made in, may have issues syncing non-standard framerates. When using vsync on a non-standard framerate, it will likely reduce the frame time as a way to sync, causing the game to run faster than intended. The difference is difficult to notice with the naked eye, but gaining a ~10% advantage in speed obviously adds up.

In reverse, running the game on less than 60 FPS will cause the game to slow down. Since this works to your detriment, it won't invalidate a run, though it'll obviously suck. If this happens, try running on a lower resolution. Some people may experience slowdown when using or not using vsync; again, if you play on a 60hz monitor, you're fine using either.

If you use two monitors, and your second monitor is a non-standard refresh rate (but your main monitor isn't), you may still experience odd behavior because Unity is stupid. You can add the line "fps_max #60" to your Steam launch options if you do experience issues (with vsync off).