To be clear, this is tied to in-game achievement "Beginner's Luck" which says:
"Have a Unique Item drop in the Twilight Strand in Act 1"
So this means you CANNOT farm Act 6 Twilight Strand for this achievement.
In order to farm Act 1 Twilight Strand, you need to create at least 3 characters. Play until you kill Hillock but DON'T go into first town because you cannot enter Twilight Strand again. Logout to character selection screen and login with another character. You need multiple characters because there is no way to manually reset Twilight Strand and spawn new enemies. Instance reset is 1-2mins so three or four characters guarantees no downtime.
Because it's luck based, this can take anywhere from 1 minute to few hours.