Tenant rights?

As long as that building is not included in your lease, you are most likely not entitled to any notice that the landlord will be there. You'll need to google and read Hawaii's landlord/tenant laws to find a definitive answer to your question.

Sounds like a separate building at the same premises...and you do not rent the other building. I don't see why he would even need to contact you at all.

He has every right. You are NOT renting the entire property, you are renting the house. He is under no obligation to tell you he is coming but he is being nice and doing so. If you don’t like it then you move.

He has every right to go to his other house on his property. Who do you think you are to imply he doesn't? He doesn't even need to give you notice unless he's going in the structure you are residing in. He's being very polite to warn you of when he will be there. Yet you complain, and he's not even there that often. If you complain be prepared for him to ask you to move. I know I would.

He does have that right, unless your lease states you have use of that structure, which is doubtful.

You rent the house; presumably this structure is separate to that.

Yes, he has the right. You were aware of this when you rented the place.

only a lawyer would know for sure

Probsbly. Your right to 24 hour notice is if he's coming into the house you're renting. Unless your lease says otherwise, he can do what he wants to with the other structure.

Yes. 24 or 48 hours notice is required for admittance into your home. You are renting the house, not his property.