I can't speak for other people's experiences but I did deploy to Afghanistan as a combat arms reservist in the Canadian army. Typically, you're expected to be overseas for 6 months but anything from 5-8 isn't that uncommon. Other roles had other expected deployment lengths. To prep for a 6 month tour involved full time training for about 8 months. This is the same training time the regular forces got and was done with them.

I think you may also underestimate the amount of training reservists do. To get fully qualified in my trade took over 3 months of full time training split up over a couple years. During my time in the reserves you'd do 1-2 evenings a week from September to May/June. You'd also have 1 weekend a month training for most of those months and 1 week long training exercise per year. During the summer, people who had the time could do full time work taking or teaching on courses.