I don't think you'd be out of line at all. It's your house and your project. Presuming that you don't hold up his schedule at all (and you've already pointed out that he doesn't work weekends), I can't imagine why there would be a problem with this. I guess the question would be, if he were hiring his paint contractor to do the walls would that person be expected to do the walls AFTER the trim work? I highly doubt it. This is no different from subbing the job out yourself, except you're subbing it to yourself.

"I'm aware that walls are done after ceiling paint, but before cabinets, trim, and floors"

There is no right or wrong order of work for painting; it is always a difficult compromise and therefore personal preferences rule. Your contractor's approach is preferred by many painters and probably all carpenters.

Perhaps you could apply the primer early but if you applied the finish coat early, you would end up touching up damage and cutting in the finish paint coat at changes in materials and finishes to get a professional looking result.

He is saying that to avoid messing up the paint job while adding the trim/flooring/etc. Painting with latex(water based) paint is much more simple than oil based paints. A splotch of paint in an unwanted area is easily cleaned with a damp rag.

I helped build over 50 HfH houses, using volunteer painters and trim installers. We always painted before trim and flooring. It is not a problem, folks just have to be careful.

I also worked for a carpet installer when younger. It is very easy to mark painted talls/trim. You just have to be very careful.

Now, on the flip side. I have painted a lot of rooms during remodel or after the house is finished. I started out painting by masking all non painted surfaces. I got to know some professional painters and found they seldom mask when painting with brushes. They do mask when spraying.

I tried cutting in without masking. It takes a really good tapered brush and some easily learned technique. That seemed slower than masking, so I did several rooms both ways.

Not masking was faster. Why? No time spent applying the tape, no removal, and no touch up due to paint creep under the tape.

New construction, I prefer to paint before finish work.

Remodeling, I just paint.

Lisa, it sounds as if your contractor does not want to get any grief if his crew mess up your newly painted walls. Construction crews can get pretty sloppy. They could easily gouge the wallboard. If you don't paint, the contractor would be responsible for fixing any gouges. If you paint, the same responsibility would apply, but I don't think you would be satisfied with their repair job. Just my two cents.

Sounds more like the contractor doesn't want his work schedule to be compromised by the owner/painter.

Been there, done that.

IMPO Contractor's biggest mistake was allowing the owner to do any of the work, but his approach for controlling the outcome by making the owner wait until he is done and gone apparently works for him.