I may be a bit late in submitting this tip, but if the Megalosaurus wakes up from torpor-inflicted sleep, the taming progress does not disappear. However, if you do not knock it out quick enough the taning effectiveness drops very quickly once it has actually been knocked out a second time, so bring taming food immediately before knockout (maybe when it's torpor running). Also, don't use sanguine until food is in it's inventory for the second knockout as the 30% drops very quickly

More Megalosaurus Taming & KO Tips