I don't quite get the customs of that time when it comes to more-than-one-wife. (I also don't get what man in his right mind would even want more than one woman? Isn't one of us quite a handful? In the Bible, every time there was more than one, all manner of problems came washing in. lol) The only part I know is usually the first mate is called "wife." All the others are usually called concubines, slaves, or servants.
My interest in multiple-wives came along with Solomon. "Wisest man ever" goes off and has a village of wives. (How wise was that? lol) How do you keep that many content? Rotate? Even if he brought one in per night, each wife only spends one night every 2-4 years with hubby. There's bound to be frustration and jealousy! Because of that, I can't see any other way but forming a schedule.
"Fairness" says make it an even schedule. ("I'm always before Joanie, but after Debbie," kind of thing.) But man has never been known to be fair, so I would think a king has his favorites. Favorites -- not favorite -- or they'd only have one wife. And since they probably did have favorites, they still didn't want to get the favorites upset without enough attention.
All we really know is he did not get around to defiling another man's wife before God warned him off.
And, yeah. I see where you're going with verse 17. Who even notices infertility in the space of one mere day? But God being omnipotent and omniscient, I could see him drying up the fertility for a year or two before this, so the king -- and his wives -- noticed something is wrong. Only to give them fertility back because the guy feared the only real God. Something like giving the effect before the cause to stop the cause. ("If you think infertility was bad, let me tell you death is imminent if you don't obey me. And, if you do obey me, fertility returns" kind of thing.)
Again, this is just a theory.
Funny thing about people. We fill in the blanks when we read a story -- whether the story is non-fiction or fiction.