Keep the conditions in proportion. Håkansson is Norwegian, he is completely used to exercising in these temperatures, and so is Jornet: the temperature may be cold for standers by, but is fine, even quite good, for running. There was a 24 hours that was in mid single digits (celsius) about a month or two ago in mid-Norway (that one of the other participants, Holvik, won, incidentally), and the conditions were described as perfect. A little colder than that where they are, but not much. Lack of wind is much more important, that is why the start was delayed.
I also know that Håkansson was fired up by some comments on a Norwegian podcast saying there was no chance they would come near the record. He is going to give this everything he has got, I am pretty sure about that. A question for me would be if Jornet drops out, whether Håkansson will be able to keep up the spirits to complete. But if Jornet keeps going, so will Håkansson unless he absolutely cannot go further, and I doubt he will drop pace much.