If "created_after/before" is used with a "time" type partitioning
column then show_chunks was not showing appropriate list due to a
mismatch in the comparison of the "creation_time" metadata (which is
stored as a timestamptz) with the internally converted epoch based
input argument value. This is now fixed by not doing the unnecessary
conversion into the internal format for cases where it's not needed.
Fixes#6611