I wouldn't feed as much as they will take in 20 mins, that's a long time to continuously feed an Axolotl. I judge the amount to feed based on the physical size of the Axolotls body and the size of the pellets, realistically you wouldn't want to be feeding so many pellets that it would fill its body causing it to bulge, then not exactly making it easy to digest, potentially causing a sort of impaction. This is just my theory though. I feed in smaller amounts but once in the morning and once at night, I like to feed only once a day if the Axolotl hasn't passed the food from the previous days. Again this is just my theory