That sounds pretty much correct. However, I don't think you can use 's' to keyframe, as that just keys the transform channels. You'll have to actually RMB > key selected over the wind attribute you want to change.
Now, in the graph editor, select the wind field, or whatever you are using to do the blowing, and you should get the attributes that are keyed showing up in the graph editor. Hit 'a' to frame all. Marquee select over all the keys (they will turn white and tangents will appear). I believe there's a menu in the graph editor called Tangents. Go Tangents > Stepped. The shape of the curves should change to straight lines, and as you play it back, the value should change immediately at the frame you set. Hope that makes sense.