King's Bounty spell question
 

I not talking about King's Bounty Legend or any of those that are fairly recent. I am referring to the one played on the Apple// - I have been reading forums and was told that if I get too many battle soldiers/units and cast "raise control", I can control that army unit. But how long does Raise Control last? I'm afraid that if I get a ton of ghosts (for example) and they go beyond what I can handle, and I cast Raise Control, those ghosts are fine. How long does the spell last? I don't want to have a large group of army units and have that new level of control run out and then I'm up the creek? Or if I cast the spell, I'm good from then on? Can anyone help me?