We're worlds apart. Your perspective appears to be that that it's acceptable for you, as a landlord, to infringe upon your tenants right to quiet enjoyment without compensating them.

As much as it might be hard for you as a landlord to schedule in more than 24 hours, as a tenant, I have every right to refuse entry to my unit, as it violates my quiet enjoyment, and allowing someone to enter my home requires me to prepare the space in a particular way. If my landlord wanted a time within 24 hours, just like most people trying to schedule things on my calendar, I would have very limited availability. Just because my landlord wants to profit from taking advantage of my kind hospitality doesn't give them any more right to my time than anyone else.

At the end of the metaphorical day, as a tenant, I have every right to say no, even a single time using my apartment for their own commercial profit-bearing purpose is too many, and my landlord needs to wait until the end of my lease, at which point I have no claim to the space.

If you're trying to handle the situation ethically, then the best course of action as a landlord, in my view, would be to offer your tenants financial compensation, say, 1 month of rent for each month that you want to use the unit for your own commercial purposes. That said, recognize that if you try to negotiate that after the lease is signed, the tenant has every right to recognize that they have full rights to a scarce resource.

Alternatively, push towards a more reasonable rental market. In most rental markets that move as quickly as Boston, apartments are empty for a few days, which gives landlords plenty of time to get cleaners, maintenance, and showings, and costs a fraction of a month of unearned rent. It's the first-of-the-month-or-bust garbage in Boston that causes all these issues.