1.5 - 1.75 hours is fairly reasonable.
I myself do Forge rushes with friends - we do these in classic - so remember u dont have to do act 5.
The rush character has all the waypoints already.
We do this :
Me using 2 computers and 4 friends using 1x computer each.
make a game with the mule ( so all quests are open )
bring in our 5 rush characters, 1 of them goes to andy sets up the first wp , the 2nd gets the magot lair chest tp , the third the claw viper temple tp, the fourth to set up durance 3 wp, the fifth to clear chaos sanctuary.
When one person gets the tp set up they leave and help the next person and so on until we have all tps and maps.
I use my 2nd computer to get all the maps with my sorc and wait at andy. So I can make up easy Tps for eveyrone.
I then use my first computer bring in my mule, everyone else brings in their mules,.
I use my sorc to give us every tp, we go down , kill andy - I port to Act 2, use my maps to give everyone the next lot of tp's, and so on.
Goto travinacle kill council, kill mephi.
we all goto act 4 and kill diablo.
Prep work - 10-20 minutes
Rush work - 10-15 minutes.
Thats 20-45 mins for each difficulty.
It can be done with a bit of teamwork