charttime records the time at which an observation was made, and is usually the closest proxy to the time the data was actually measured. storetime records the time at which an observation was manually input or manually validated by a member of the clinical staff.
Histogram of differences between charttime and storetime where charttime > storetime:
How do we interpret events where the observation/measurement occurs after it has been manually input/validated?
From the docs (https://mimic.mit.edu/docs/iv/modules/icu/chartevents/):
Histogram of differences between charttime and storetime where charttime > storetime: