Contrary to popular belief, lactate dissipates fairly quickly after exercise. Even if elevating one's legs speeds that process, it's unnecessary.
Elevating one's legs, like applying ice, is very helpful for reducing inflammation, however. Within 20-30 minutes after a hard workout, I wrap my medial shins (where I tend to get sore) in cold packs and prop them up a little higher than my body for 15-20 minutes. Sometimes I repeat this after a couple of hours. I believe this practice has helped reduce my soreness and speed my recoveries.