I used to refer to this time frame as "the witching hour". Pretty much the time before dinner to before bedtime. I saw it with both my kids so there must be something to it. They can be perfectly happy all day but then by the time it's time to start preparing dinner, Daddy gets home, and we start wrapping up the day-- you'd think all hell had broken loose!
Babies and kids can feel your stress too and on top of trying to process a busy and active day they had themselves, they are VERY prone to meltdowns and tantrums at any age.
Try to stay calm yourself as you get your son and are prepping dinner. I know it's habit to feel rushed but try anyways. You'll both be in a better mood for it and more likely to enjoy each others company.
If it's a nutrition issue you're worried about, I would tweak his meals that you provide to the daycare and ensure that he gets most of his proteins (or veggies) whichever you feel he lacks, at lunchtime. This can be his "main" meal for the day rather than dinner that is too unpredictable for nutrient intake. I still wouldn't feed him junk for dinner but if he gets a yougurt or string cheese eaten (protein) or a few bites of deli turkey in his belly with some applesauce or carrots to munch, he's doing ok. Don't expect him to eat a full six course meal-- his tummy is only as big as his fist. So don't feel like you have to pile food in him, especially if he eats alot for lunch!
Good luck and I hope this helps!