But the comment says it would apply to buildings with over 10 units. So, for a building with 11 units, that gives 132 unit-months per year. With a maximum unoccupied rate, that’s 6.6 unit-months per year.

As the renter, I’d really appreciate my landlord wait until I’ve actually moved out to start showing my unit, although they don’t always do that. Assume all 11 units decide to move at the end of their leases, that means the owner has a little about 3 weeks per unit to clean, do any maintenance and repairs, and find a new tenant. If the unit needs extensive repairs/cleaning, the owner probably doesn’t want to even start showing it until the repairs are completed. Hopefully most tenants renew their leases and stay longer than 1 year, but the owner can’t count on that. Even on a larger building, the numbers still average out to 3 weeks per unit, but at least the effect of a few extra non-renewals is smaller.

I think a 90% occupancy rate would be a little more realistic, but would probably still need some room for exceptions.