Some of these suggestions are probably better suited to a town-and-a-dungeon game than a West Marches-style hexcrawl. Our solution back in the day was "keep playing until the PCs get back to town."
I thought about doing something like this, but it does run counter to one of the primary conceits of the West Marches game. I've got quite a few potential players for this but they're all casual gamers and attendance is likely to be patchy. I think it's fairly essential that we can have a different party for each session, and the "keep playing" or "basecamps" options prevent that.
I'd go with an "escaping the wilderness" table and just make it more generous than the "escaping the dungeon" one."
Yeah, perhaps this is the answer. As you say it does make sense for the return to be a bit easier, both in terms of the fiction (you know the way and the dangers) and narrative pacing (we've already told this story the other way round!)
Wilderness exploration -> a cursed fog either inhabited by monsters or causing madness, visible on the horizon
-> roving army of gnolls/orcs/goblins that could descend at any time, war-horns can be heard minutes before they appear
Cool, I like these ideas. I mean, at its simplest it could just be that being out in the wilderness at night is a *really* bad idea...but the warhorns thing is cool too

I don't think so. We would do 7 pm to 11 pm at which point the horn would sound. Then we have that last hour to wrap up. An hour is plenty of time to resolve one random encounter plus end of session discussion. Sometimes they'd even fish for a random encounter if they were close to leveling (go slow pace, track to find trouble, etc.).
So yeah, the issue I have is that we have some players who don't get back from work until 8pm; we have a 1 hour time zone spread, and we have some for whom a 12pm finish is pushing it a little. In the worst case we could easily end up with a 2.5 hour session - which means that it's going to have to be pretty fast-paced to be worthwhile. In true WM style, all housekeeping/downtime is done between sessions, and I'm anticipating doing a fair amount of quite aggressive narrative framing to keep us in the action, and a "decision countdown" in combat to prevent us getting bogged down. Even so, two fully-played wilderness travel segments may end up being too much....