Campaign games for solo, what is your sweet spot in terms of length?

I find myself more or less hoping for fixed game lengths when it comes to campaign games... at least int he board game realm. I've always felt the Pandemic Legacy games were a good sweet spot for a campaign (12-24 games) but I haven't played any good truly short ones yet. I have Legacy of Yu on my soon to play list, but what others might be shorter.

And of course, what is your sweetspot for campaign length?