Hunter Killer Earn x number of Combat XP 1 satr=6,000 2 star=8,000 3 star=10,000
Combat xp is some of the least predictable xp in the game. In an even match you might get a little under 2000 xp (about 10 kills), if you are rolling the other team you might get more and if the other team is good or rolling you then you could easily earn much less.
Given this the hunter killer mission might take 4-6 matches to complete. If each match lasts about 20 minutes that's 1:20:00 - 2:00:00 hours to complete. If you manage 15+ kills per match it will be faster but most people don't.
I would consider this too long especially considering if you play well with any other mission you can complete it in one match.