Apparently you can repeat this mission as many times as you want, as long as you don't turn in the quest at Fleet Admiral Tethys... basically you can get 1 bar of XP every hour without doing anything. It will probably be fixed soon.
Still not fixed as of December 21th, 2016.
I'm having a listed success chance of 134% but I've gotten the bonus five out of six missions.
Could be shear luck or a bug since the mission is almost certainly bugged aswell.
Came here to find the number of missions needed to complete.
Garrison Timer Mobile App
[Upon completion your 勇士 will gain: ]
Legion Class Hall Mission Guide