I don't think this is nearly all signal-less; Black Market is exactly where I'd expect it to be. But yeah, looking further down the list leads to rarely-bought cards like Navigator and Venture that seem to be mostly the noise of the rest of the kingdoms they happened to be part of.
Well, I agree that I'd expect Black Market to be near the top most time-consuming cards, but we can't just look at the list and conclude that the parts that we already expected to see are signal and the unexpected parts are noise, and then use that as evidence to reaffirm our expectations.
Short: I dug into those Venture games and discovered one reason that Venture does make games longer: it's from Prosperity, so Venture games are more likely to be Colony games! However, that's a fairly small effect, but it did happen to be noticeable in a couple of the games I played.
Long: So let's dig into those games to see if those cards mattered! For instance, let's look at Venture, which I don't expect contributes to the signal. We'll focus on the games with Venture in them that were longer than the median to see if it had an effect.
#17259294 vs Philip (37:09) - a Hamlet-Watchtower engine on a Pooka board that piled Curses, Hamlets, and Farmer's Market's. One Venture gained and subsequently trashed to Salvager.
#17395519 vs Jangus (36:34) - a Herald-Jester-Courtier engine with Forge trashing. One Venture gained by Jangus, I have no idea why.
#15876496 vs f_____t_ (35:43) - the most notable thing about this game is that 5 Ghosts were gained, 2 by me and 3 by f_____t_. No Ventures gained, though, even though they can be trashed to get a Ghost.
#17812665 vs Obi Wan Bonogi (30:29) - a Colony game where Crossroads, Magpie, and Necromancer piled with 2 colonies left. No Ventures gained. Rabble also on the board so unclear if Venture caused it to be a Colony game.
#16172946 vs yudai214 (29:59) - another Colony game (with Venture as the only Prosperity card). One Venture gained by me, no idea why.
#17255797 vs Philip (29:51) - a Page game with Necromancer/Secret Passage for trashing and Dominate to build to. One Venture gained by Philip, no idea why.
#17145573 vs nasmith99 (24:22) - Ambassador war fought closely, Menagerie, Wolf Den, Grand Market. No Ventures gained.
So at most 1 Venture was gained in each of those games. That said, one or two were Colony games because of Venture, which will happen about 10% of the time Venture is on the board. And indeed, Colony games tend to be about 3-4 minutes longer on average:
Type | Count | Average Length |
Normal | 396 | 18:24 |
Colony | 31 | 21:51 |
Shelters | 40 | 17:28 |
Colony/Shelters | 4 | 14:36 |
So my conclusion is that there's a tiny signal just from Venture being in Prosperity, but its position is mostly noise.