pydata/pandas — comment on commit 4ec8e40affd7028a78b9472bf3ad5ac69ca63f91
File: pandas/src/datetime.pyx line 1621
By adamklein:

I was thinking about this section. If it becomes a performance bottleneck, we could have a structured dtype (Y/M/D/h/m/s/us) backing the dt64 index, built & cached first time we need access. Getting at fields then becomes down to nanos.