I would think (hope someone more knowledgeable can confirm or deny this) that just 4 feeds in 24 hours would be a bit low for a 5 month old bub.

My baby was the other end of the scale but was still feeding around 10 times a day at that age.

On the weekend can you put bub to the breast more often? Even if he only has a small drink in the middle of the 4 hourly usual feeds, every bit will help. Could your DH similarly offer a smaller feed between feeds or do 3 feeds during the day of slightly smaller bottles instead of 2.

I am so inspired by full time working Mums who breastfeed. Just want you to know that.