Uhh, hard to say how long it took me. Prior to 10.2 I was working on like 7 different characters at once, since all I was doing was the handfull of world quests that gave 376 gear at that time, it was like 30 min per character at the time. I was basically just seeing which character would get a full set of gear first, and then level them to 60, many weeks I would get nothing.
When 10.2 hit and all the WQ updated to level 70 rewards, and it was discovered that bags dropped 418 gear, I swapped to bag farming on a single character and spent a few weeks casually farming bags with a group that did call outs and invites to shards with active hunts.
Some days I farmed none, other days I copped like 50 bags in one day.
According to my Discord logs, I farmed bags on my DH from Nov 13th to Dec 2nd, so about two weeks.