I know chronology on a story this size must be tough, but there seems to be a slight discrepancy concerning stannis and the wall. Now, the others attack the fist not long before the wildings show up to find the remains.
Sam sends off a raven and in turn ravens are sent to the kings asking for help. It appears that the message has been on dragonstone for some time, before Davos finds out and decides to act on it. Now judging from the maps, and the timeline i've got in my head, there is no way that stannis would have made it in time to save the wall from the Mance.
Here's my take, maybe you could correct me if i'm wrong.
-Others attack the fist, sam sends off a raven, a few days later it reaches the wall.
-a few days later the wildings come upon the fist, probably about the same time the raven reaches the wall.
-messages are sent to the kings, judging from the distance in the maps, stannis receives the message 1 month later.
-Jon scales the wall and a week to 2 weeks later he gets back to the wall. I'm sure by this time the raven hasn't reached stannis or is just reaching him.
-let's say for example, the message wasn't brought to attention for a couple of weeks, then Stannis sails from dragonstone, takes app. a month to reach eastwatch by the bay. Takes another few days to reach castle black. so if we add all that up, stannis is late by about a month and a half.
The reason I am never specific about dates and distances is precisely so that people won't sit down and do this sort of thing.
My suggestion would be to put away the ruler and the stopwatch, and just enjoy the story.