If that is the case then I assume that if there are no allied casters, they belong to barbarians, so the turn of MK starts as soon as the day starts (if I recall correctly, barbarians go first?).
Also it means that the spells duration is measured by unit the spell is cast by. Otherwise it would be kinda foolish, like calming down Jojo on his turn while it was "yours" and the spell would start working on his turn, but since you are engaging, then he still can protect...
MK sure is messed up place.
A side thought, how do sides with no casters purchase services of MK? Lets elave out Charlie (he pops only arhcons who are avian knights or something like that, but not casters, but he has thinkamancy). I mean how do you hire a caster, if you do not have a caster to enter the MK in the first place. And you do not have a caster to send a thinkagram to MK to hire a caster? Then again, perhaps natural leader thinkamancy can do that?