*many sighs of relief* It only took me... a year and 3 months lol.
Woot! Dutiful companions collected!— Quintessence (@perksnpeeves) November 24, 2017
(ノ^ヮ^)ノ*:・゚✧ pic.twitter.com/DDG5qGugNw
For those still working on and/or dreading the Prestige grind, don't take how long it took me to heart. I wasn't consistent and periodically took LOTS of time off from doing PVP WQs.
If you do 3 Towers plus at least 1 FFA WQ a day (with Battle Standard of Coordination dropped for all of them), it will take you roughly 178 days (or about 6 months) to reach Prestige 7 from scratch.
Here are some numbers (this Wowhead PVP guide is useful):
Prestige 1 - Alliance Enthusiast and Horde Fanatic
Honor 0 to Honor 50 (first time) = need 22,000 Honor
Prestige 7 - Dutiful Squire and Dutiful Gruntling
44,000 Honor for each Rank after x 6 Ranks = need 264,000 Honor
22,000 + 264,000 = need 286,000 Honor total
Honor Earned Daily
PVP Tower WQ = 345 (with Battle Standard)
PVP FFA WQ = 575 (with Battle Standard)
345 x 3 = 1035 + 575 = 1610 Honor earned daily
286000/1610 = ~178 days to Prestige 7
If you do battlegrounds/arenas, you can earn even more and the grind will go even quicker. However, the PVP WQs are just the basics and bare minimum.
6 months may seem like a long time, but considering the current estimation for the next expansion is some time summer of 2018, if you were to start the Prestige grind RIGHT NOW and stick with it, you should earn Prestige 7 before Battle For Azeroth.
Also, keep in mind that Blizzard's current plans are to keep these rewards post-Legion. They might not, however, be earned in the same method as currently, in BfA. We still don't know how they'll be awarded in the future, but at least we have peace of mind that they will not be Legion-exclusive.
If you can't earn these companions now, you *should* be ok and have the opportunity to (possibly in a different way) in the expansion. !!! DISCLAIMER !!!: THIS IS SUBJECT TO CHANGE AND NOT SET IN STONE; complete the Prestige grind or don't using your own discretion.
Some tips for grinding to Prestige 7: