Each ankle sprain is different, some a lot worse than others so its hard to pinpoint exactly when you can start training again. If there is no bruising I would say its only a mild sprain, probably a few weeks rest, but i'm no expert. Its been a month for me now with no running whatsoever, but plenty of stretching exercises, also been doing a lot of cycling, hoping to get back running in a couple of weeks, starting off nice'n easy on the treadmill.