This server-side mod pauses timer when you enter vault and resumes it after you move certain distance.
Default distance is 18, which is enough to allow free movement in the first room. (this is 2D distance, so you can be at any height)
This allows you to let the chunks load when you are in the first room without losing vault time.
Please report any issues (like timer not starting again) here.
Unfortunately you will most likely still lose few seconds due to how the timer works.