time counting down slightly too slow

[Nicknack32]

Hello, I am trying to build a 60 minute countdown timer for an escape room, and I am having issues with the timer. It appears to be running slightly slow. By my tests, if I speed it up 1.2x it will just about perfectly count seconds.
Im not sure if its all the other code controlling other parts of the timer that slows it down or what.
Any input on how to speed it up accordingly would be appreciated. Thank you.