After we merge #55559 we'll have a few things to clean up:

• Implement interval rounding (Speed up time interval arounding around dst #56371)
• Cache LocalTimeOffset.Lookups to avoid building them over and over again. They are quite expensive to build and would likely cache very well.
• Investigate how expensive loading the min and max is. Maybe we can cache them on the reader or something.
• Plug this in to auto_date_histogram. It could speed it up a ton. (Speed up rounding in auto_date_histogram #56384)
• Remove the optimization that rewrites non-fixed time zones into fixed ones in date_histogram. It won't really do anything after we get interval rounding. (Drop rewriting in date_histogram #57836)
• Speed up nextRoundingValue to make date histogram on date ranges faster.

Maybe:

• Plug this in to composite. It might not benefit much from it but then again it might. It is worth checking.