When Rab first came out, it took like... two hours to finish (I might be exaggerating... I hope I am xD), but now it's a breeze. I think when people get more and more familiar with Rid like they did with Rab and other raids, it'll probably go by a lot faster. Like, with what Enla says: getting DPS buff, not dying as much, et cetera, may drastically cut the time it takes to finish Rid.