So, assuming you have the research passives maxed in the craft ... and are diligent about keeping the timer going every time a piece is researched, it should take about 9 days per gear piece.
Remember that you can only research three (3) pieces at once with the passives fully maxed. So, a five piece set of Hunding's you add "round 2" for 9 days. Approximately 18 days for the full 5-piece set.
Hopefully another forum-goer can check my math just to be sure ...
Yes, but that's the "minimum" answer, and the question was average. The issue is going to be the availabliity of research pieces for the traits wanted. If you don't have a piece in your inventory, you can't start the research. And the set you eventually make will have one of those six traits on each piece, so you also need to ensure that's one of the ones you research.
But it won't be a lot more than that 18 days., if you're prepared to either buy pieces, or beg a friend to make you research items. They only need to be white quality, in iron/rawhide/homespun/maple, with the trait you want to research.
Remember, too, that the timer will elapse at inconvenient times, like the middle of your sleep. You won't always be there to start another round. And RNG will have you run out of some material just when you need it!
If you have a good guild, or know a crafter, you can ask for trait research pieces to be custom made for you. You want to craft Hundings for your character to use, and you want training on every piece, you can ask the crafter to make all training trait research pieces for you. Or whichever traits you think you'll be using the most, so you can get them researched first.
If you're serious about researching as quickly as possible, there are also the instant research scrolls from the Crown Store. And don't forget that a five-piece set isn't necessarily made up of five pieces of the same type of gear-- for instance, it could be three pieces of light or medium armor, plus a two-handed weapon such as a battleaxe, maul, greatsword, bow, or staff, or even two one-handed weapons, or a one-handed weapon plus shield, or two items of jewelry, and various other combinations.
So the minimum would be 9 days, not 18 days, which could presumably be shaved down to less than one day if you bought enough instant research scrolls.