This might need correcting in the future, as to me it showed with a duration of 16 hrs.
besides that point, I logged out of this character to log in to another while waiting out the time. I am sure I logged in after at least 12 hrs, but when I checked to see the time it was around the 8 hrs mark.
I don't mind if you downvote this, but please reply to this comment if you experienced something similar.
Garrison Timer Mobile App
[Upon completion your 勇士 will gain: ]
Legion Class Hall Mission Guide