Set script to run only between certain times of day

[PAGWatson]

For example, I use the script to sync my work calendar to my phone's calendar, and I don't normally need it to run outside work hours. Google have sometimes cancelled the script's trigger due to it using too much compute (when I had set the update interval to be quite short), so this may give a significant compute (and environmental) saving.

A simple thing may just be to have startSync start by checking the time and exit if it's not between the set hours, but maybe there's something cleverer that can be done with the trigger.