I'm not gonna update this because there's now a built in functionality for this purpose.
Hold Ctrl and Shift and click the Settings menu, you're gonna see new tab called "the rest"
In it, search for "ambient-music-pause", you will see 2 options.
'mean' is the constant, minimum time of a pause
and
'variance' which is the random addition to the mean (if I understand correctly).
You can also scroll a little lower and get to the music transition delays so it's not switching the music all the time. I have the delay-ticks set to 999999.