Well, something weird is going on. I was absolutely paranoid about post-publish testing of a new mission called "The Dance of the Dead." It should take at least half and hour, but more like 45 minutes.
My first 5 reviews (in the review stage) were 4 complete playthroughs and 1 guy who had to drop because a npc was nowhere to be found.
My mission didn't qualify for rewards until it had 24 plays. It would be impossible to play this mission in less than 15 minutes, even if quickly pressing f at every spot of dialogue.
Average length of mission is not the only factor used in determining whether a mission qualifies.