I wonder if we need this flexibility right now. Do we use `DateRangeFilter` in multiple places, with multiple/different buckets?

I might consider just bringing this logic into the `DateRangeFilter` class itself. At that point, you need no lambda and it doesn't matter where you instantiate these classes -- that means you could hold already-instantiated instances in `FILTERABLE_FIELDS` (perhaps giving it a better name) which I think would simplify some things.

Just a thought...