Yes, that is right. After a normal shock there will not be any visible sign of mustard algae, but it is actually still there. The an extra 24 hours at exra high shock level will get the last hidden bits of it.
No, it is unusual to see CC at that point. Check the CC again when the 24 hours are up and if there is still CC > 0.5 you will need to continue shocking (though you can go back down to normal shock level at that point).