Well, depends on what you want to do with the data. In this case, since it seems that the end goal is to get an average, I would probably recommend system.tag.queryTagCalculations().
A tag history binding on the table might also be acceptable.
For reference:
It isn't just 12 hours once though, its the last 12 hours. Which to me means that it is rolling, and so unless partitioning is off completely, at some point the query will break.