Snacks at 10m

My twins are 10m and on a combination of breastfeeding and solids. Right now they get 3 meals a day and I am wondering if I should do a snack after their afternoon nap cause they get really fussy around 5 pm. I breastfeed on demand throughout the day and night but I also have low supply. Anyway, our schedule looks like this:

7 am wake up

7:30 am breakfast

9-10 or 10:30 nap

12 pm lunch

1:30-3 or 3:30 nap

6 pm dinner

7:30 bed