I did 24 hours and he was still reacting. But it may not be due to the milk but rather that it takes a while for the reaction to leave his system. Sometimes when my son reacts to something, it takes about 3 to 5 days before his skin is cleared again.
My kids had rashes that cleared up w/in 3 days. Gassiness was improved w/in 24 hours. Never really cared about their poop, it didn't make them miserable. DS might have still had blood in his poop for a few weeks while things healed.
Re: Milk sensitivity