I am surprised multiplayer is the issue.
It's not *the issue*, it's (potentially) *an* issue.
I don't see why people in group aren't just "on the same clock" regardless of where they are.
If two players are in the same party then I would expect them to mostly stick together.
Frankly, I'd put them all into turn based combat once combat began. It's what I do in PNP games when groups split. I bounce between the group until combat starts... at which point everyone is in the init order and can act only on their turn (even if they're really far away from the action.)
I know they don't want players to be ridiculously far away and unable to make it to combat, but I don't have a problem with that. Groups should stick together if they want to support one another. And if you're not, there are consequences.
But, that said, even if they wanted to give players that were a certain distance away "double moves" so that they have a more realistic opportunity to get into combat faster (combined with allowing waypoint travel when a certain distance away) they could mitigate the issue enough as far as I'm concerned.
So... yeah... that's not really one of the more complicated issues with day/night cycles.
