Short of setting up a video camera, I don’t know how you would know

Most bunnies sleep during the day and are active in the mornings and evenings. That’s their natural way, and it makes them excellent pets for working people.

Well as said before rabbits sleep during the day. Try purchasing some toys for your rabbit to play with. Sometimes I take the left over toilet/paper towel rolls (the cardboard part) and fill them with hay and then close them shut on either side. Or just the roll. I have even used cardboard boxes from when I get things from Amazon (I take the tape off and any stickers). I even use paper bags that I ask for when I go grocery shopping. There are so many different things you can get that your bunny can play with, and you don’t have to spend a fortune on them! I hope this helps!

Twigs of apple or willow are good too. It’s a healthy snack as well as an activity to gnaw the bark off (or even chew up the whole thing like one of my buns does.)
If he doesn’t have a cardboard house (upside down cardboard box with door-holes) you could give him one, they like to re-model (“bun-struct”) cardboard houses and can use lots of time and effort on such projects.

But honestly, I think if you concentrate on letting him play and be pet and have bunny-fun when you come back home in the evening, he’ll be happily sleeping all day long while you’re gone. Rabbits are crepuscular animals, which means animals that are most active at dusk.

Willow balls are a favorite. I also weave cardboard through the bars of the cage and twigs-I have pear, rose and blackberry branches I use and weave through the bars.

I use chunks of wood with holes drilled in them that I string safe rope (hemp and sisal) through, or tie to the side of the cage, or stuff some hay in.

if yours likes to throw things-plastic balls and baby keyrings work too.