He does this a lot. Advice?

Again, no rhyme or reason when Dementia is involved. There are microwave plates with sections and lids. If he doesn't want to eat when u do, put the lid on and put in frig.

I like the idea of "pretending" you are having dinner much earlier than you actually want to serve dinner. Maybe that'll work!

Per your profile - he works out 3 - 4 hours a day?? That's a lot! What is he doing? I'm sure he is doing better due to working out!

Caring for Alzheimer's patients is not for amateurs.

If the original plan is to eat dinner at 6, then push it back to 5; when DH tells you he wants to eat dinner 'after you've put everything away', that will be at the normal 6 pm dinner time. Either that, or when you're putting everything away, prep him a plate and put plastic wrap over it. So when he asks for the food later on, pop it out of the fridge and warm it up in the microwave. You have to roll with the punches with Alzheimer's, otherwise you'll be going out of your mind ALL the time. Find work-around's for your own sake that keep HIM happy and you from tearing your hair out!

Good luck!