Heat extracted I seem to do well with about 24 hrs. Then I let it sit and cool for several hours before filtering but that's usually because of my schedule (and sleep)
Been learning the heat process from reading this great thread, from my newbie experience (12 pipe tobacco extractions so far + 4 cigars going on right now), the strong pipes tobaccos like Nightcap, Bayou's, Billy Budd, Havana Daydream, Turkish, Orientals and all the English blends don't need to my taste (I like strong flavors) more than 10 to 12 hours continuous heat assistance. Unproper after taste and parasitic taste appear on my first 4 batches after 12 hours at 55°C heating. Done them for only 9/10 hours and was perfect. For peak strength tobaccos like mainly virginias or RYO's, 12 hours seems to be more than enough in what relates to me.
For the cigars I don't have any experience yet, just started 2 "acids" and one Rocky Patel yesterday. They got 10 hours heat + 9 hours cold yesterday, I will give them 12 more heat and 12 cold today and I'll see if they'll need a bit more. They smell fantastic at the moment.
I've also asked weeks ago on this thread to be sure if we should make the heat extraction with jars lid on. The answer I've received was yes. So my first 4 extractions were lid on. Not happy at all with the final result, much to strong concentrate with parasitic taste. My other batches were done without lid. The result is perfect as far as I'm concern.