I posted a guide for that in: Season 22 Solo HC Leveling Start Strategy - Demon Hunter - Diablo 3 Forums (blizzard.com)
It really depends if you’re doing HC, SC, and if you’re on the PC or console.
For SC on the PC, just run T6 HoA1 traps. This is dependent on how lucky you get with the map layout, and how familiar you are with it. The first 12 levels can take as low as 4 minutes.
For SC on the console, HoA1, but you want to use the fire pits to kill, as the traps don’t work nearly as well. Or you could use the HC approach, which is slightly slower, but vastly more consistent.
For HC, Eternal Woods, then switch to the campaign (yes, the campaign), and use the Mira trick.
This is the first 12 levels in hardcore. It takes me roughly 12-15 minutes, though your mileage may vary:
A full SC run I recorded in roughly 75 minutes, using only Lord Greenstones Fan. (I.e. No legendaries nor ruby in helm).
A full HC run I recorded in roughly 1h50 minutes, using only Lord Greenstones Fan. (I.e. No legendaries nor ruby in helm).
A full SC run on the console I recorded in roughly 1h55m minutes, using only Lord Greenstones Fan. (I.e. No legendaries nor ruby in helm).
SC is fairly consistent for me, both on the PC (roughly 75m) and console (roughly 2h). You’ll notice the console takes far longer, because massacre bonuses work differently there and put you at a significant disadvantage. HC works for me about 7/10 times, and is super scary, unless you’re use to it. I would not suggest doing what I did unless you’re very comfortable running it.