I think this is actually the underlying motive.
OP thinks her ex is wanting to date, and it's rubbed her up the wrong way. He probably is, and generally needs one weekend night to do so... And he currently has the child every single Fri, Sat and Sun night.
Now he's reduced it to every single Saturday and Sunday night.
OP's thread starts, with her shock that whilst he works full time and she works zero, that he is "only" having their child 3 nights a week, compared to her 4(!) and that she is unhappy that he might drop to 2, in the name of tiredness. However, she then later reveals that if she loses children time at the weekends, when can she go out and date? So it would seem she wants DS out of the way to facilitate that. When, even on the reduced timetable, she has from Sat 5pm to Mon 2pm entirely child free, plus every subsequent day when he's at school.
It seems that OP suspects the ex has met someone, and OP is not happy that she hasn't yet, so wants to hinder the ex, whilst optimising her chances.
I don't doubt that OP is tired. The ex is probably more so. However, I think the driving force is jealousy.