Some thoughts on T:R's "legs"....
Legs have nothing to do with staying in the top spot -- it has to do with staying relevant at the box office for an extended time.
T:R opened on Nov 3, in the US and on Monday January 1st 2018 will have been out 60 days.
Historically the box office drops big time after the kids go back to school and the holidays are over.
GotG2 in days 1-59 (8 full weeks and the 9th weekend) had made $383,383,000 million and days 60-140 made an additional $6,977,000 million.
SM:H in days 1-59 had made $324, 085,000 and in days 60-122 has made an additional $9,948,000 million.
So SM:H had made 97% of it's USA money by it's 8th weekend and
GotG2 had made 98% of it's money.
Despite the fact that there will be two blockbuster movies opening from now until January Thor should remain in the top 10 and relevant -- unless for some reason it drops off a lot from competition from dramas and comedies and small budget action movies.
I think opening the first week of November is kind of smart. You get 2 full months that are loaded with holidays and long stretches with school out. And by January your movie will have made all the virtually all the money it's going to make anyway.
Here's a Wikipedia link to all the movies being released in 2017 and if you scroll down to Nov-Dec you see what the competition consists of.
https://en.wikipedia.org/wiki/2017_in_film#October.E2.80.93December