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Many reports related to the general topic of how to define zero energy buildings have been published. NREL seems to have spent a lot of time on the topic with:

A Common Definition for Zero Energy Building https://www.energy.gov/sites/prod/files/2015/09/f26/bto_common_definition_zero_energy_buildings_093015.pdf

Zero Energy Buildings: A Critical Look at the Definition https://www.nrel.gov/docs/fy06osti/39833.pdf

Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options https://www.nrel.gov/docs/fy10osti/44586.pdf

I think your idea is interesting since it accounts for the utilization of a building and rewards buildings that are utilized more but I think the difficulty you would find is how to clearly define the number of hours a building is used. That is often a soft number. An office building can say that it is open 6am to 8pm even though most employees only work 9am to 5pm. Someone will work until 8pm, does that mean the building is really being utilized all those extra hours? How about an apartment building? Does it have 24 hour operation even though for many hours of the day only a fraction of the peak number of occupants are present. I think you will find that almost no buildings have a clearly defined hours of occupancy.

Further, for rating purposes, the owner of the building will argue that the building is open and available to be used for many more hours than it might be just because the want to lower this metric. Allowing the owner to have direct control over part of the metric, other than energy use, seems like it is fraught with problems.

Overall, I think this approach has some potential but defining the number of hours is going to be difficult.