Redness during and immediately after pumping is not bad as long as it doesn't last very long, it's purple you want to avoid. You don't ever want to let them turn purple inside the domes, and if they get any red dots (blood blisters, broken surface veins) that's a sign of over pumping. As long as they're not turning purple or getting red dots you should be just fine. Not sure about the time though, it takes a little while for the suction to do it's magic, not sure if 20 min at a time is enough. I know some do 20 min a day once they've reached their goal to keep them topped off, but I'd try to do at least 30 min at a time while you're trying to get them to grow. Just a heads up.