Too much or too little stimulation?

My wife and I adopted a shepherd mix 2 months ago, who is now 7 months old. He is our first dog so we’re not quite sure if he’s getting too much or too little stimulation for his age.

A typical day for him starts around 5:30am with potty time and breakfast, followed by a 25 minute walk around 6:30-7. He then typically will relax until around 11a, which is when he gets some backyard time and a puzzle toy. Then it’s back to relaxing from maybe 1-3. Second walk of the day comes at 4 and is anywhere from 20-35 minutes, followed by dinner. He’s generally awake the rest of the day until 7/7:30, at which point he sleeps basically through the night (with just a potty break when we move into the bedroom around 9:30).

The problem is that like half of the days around 6:00a, 3:00p and 6:00p, he turns into quite the menace. Chewing on things he shouldn’t, getting a bit nippy, and constantly asking to go outside just to find/chew things he shouldn’t.

We do mix in training and play (which for him is mostly just chewing lol) and he’s only crated if we have to run errands since we work from home. However, if we miss a walk or if he doesn’t get his typical amount of nap time it tends to be worse.

I guess I’m just curious if this seems like enough exercise and stimulation or not enough? Should he be sleeping more or less throughout the day? Or do we just need to try mixing it up more (as much as we can at least with work considerations)?