I was doing some research on child walking speed and I also found a link that approximates when Frostbite would set in.
Im not sure if I did all this correctly but here is what I determined.
From the first link, it says:
"children in kindergarten through sixth grade. The mean speed to walk 50 ft used by kindergarten line leaders was 13.5 seconds"
So here is the calculation I did to convert it to MPH.
(50 feet / 13.5 seconds) X (60 SECONDS/MINUTE) X (60 MINUTES/HOUR) X
X (1 Mile / 5280 feet) = 2.52 MPH
So then to convert to how long it took to go 0.7 miles to the Van.......
(0.7 miles / 2.52 MHP) = 0.277 hours, which is 16.62 minutes which we can round off
to 20 minutes to make it simpler to think about.
So then, I went to the 2nd link and
from the second link, there is a graph that shows Wind Chill and
it also shows color coded Frostbite times in 3 different
colors depending on temperature and wind speed at the bottom of the color coded chart.
So assuming even a 5 MPH light breeze, at 17 degrees we can safely say we are in the White Color
which says Frostbite would set in at around 30 minutes at those temps.
So I think it is safe to say his hands would be getting very close to frostbite if not already frostbitten by the time he reached the Van. Especially if he took longer to get there or if the wind speed was more like 10-20 MPH wind.
http://www.ncbi.nlm.nih.gov/pubmed/16357662
http://timberlinetrails.net/ClimbingHypothermia.html