The way I've thought about it is when I'm "salaried" I'm being paid for my brain, not my time, and this cuts both ways; if I can meet the goals the company has set for me in 5 hours, that's all the time I'm going to take. However, if I need 50 hours to figure something out, that's what I'll do.
The understanding I expect to have with my employer is that I expect them not to give me more work than I can reasonably do in ~40 hours, on average. It's not a cut and dry calculus, but if I feel I'm being given more work than I agree to do, that starts a conversation.
I could see the role you're looking to fill being something similar; the agreement you have with the employee is that you, the employer, won't put more things on their plate than they can generally handle in 2-3 days of working each week.
The understanding I expect to have with my employer is that I expect them not to give me more work than I can reasonably do in ~40 hours, on average. It's not a cut and dry calculus, but if I feel I'm being given more work than I agree to do, that starts a conversation.
I could see the role you're looking to fill being something similar; the agreement you have with the employee is that you, the employer, won't put more things on their plate than they can generally handle in 2-3 days of working each week.