As soon as the snow is mostly gone. I love the high timber, and i'll be there even if i'm not scouting. I'd say i'm there at least 250 days a year watching muley's and elk. The best time to scout is during all the hunting seasons. Watching what they do during hunting seasons is invaluable.
The more you learn about your prey. The better hunter you'll be. Seeing how they live on off season, and hunting seasons help you get to know how they're thinking. After awhile you can almost think like they do, and be pretty accurate on what they'll do in different conditions.
Of course not everybody can spend that much time in the mountains. I've been retired for 15 years, and I have the time. However, when I was working I had it worked out so I could take off 1 1/2 months for hunting. Most all that time was spent scouting.
Looking at maps are helpful, but it can't compare to boots on the ground.