how long diablo down?

Anyone know how long diablo 2 will be down with update? and when it starts?

It isn't down.

They just took down individual game servers for maintenance/rolling restarts as they regularly do.
Join a new game and you end up on a different server not currently marked for a reboot and you're good.

Unless there's another downtime coming up that I haven't seen anything about yet that is. Either way, afk in game as I type this so no downtime atm.

Yeah, when you see the "Realm is going down in X minutes" message, it typically doesn't mean that ALL servers in the region are going down, just that some servers are going down (like the one you are currently connected to). If you make a new game, it will always (I think) make the game on a server that is not going to go down any time soon.