yep generally every hour i will do a focus, and as the qhy filters are par focal and my fingers are only so accurate i don't bother focusing between filters as the newt has a CFZ of 47 micron..... Im not that good
I stop going by the hour when the evening temp doesn't vary more than about 2 deg C between the hour interval as everything is pretty much at thermal equilibrium by that stage!
On the nights where i set and forget eg running man, that was 4 hrs of data FWHM went from 3.2 upto 3.9 which is bugger all difference at the end of the day but i did set it at about 00:30 and it stopped at about 04:00. Maximdl also has a sweet little feature that monitors the FWHM of every image that comes in and graphs it for you so you can quickly see if your focus is drifting!