My basis is the Norwegian and Swedish media, about the likes of Sundby who was one of craziest of the whole xc skier group, having been up to 1100 or even 1200 hours a year, but then went back to 800-900 at times. There have been many who state at the beginning of the season that they have trained more than ever, only to end up in 30th, 40th, 50th placings in the actual races.
From November to March, there are about 30 world cup races per season, in maybe 15 locations around the world, usually something like 3 weeks of competitions, 1 week off, with a lot of travel and recovery involved as well. In addition, there's the national championships and such. One would think that training 25+ hours a week, every week, during the racing season would be stupid.