Wojtek <wojtg(at)polbox(dot)com> writes:
> Why is the "result" incorrect (off by one day)?
> When I do the exactly same arithmetic using timestamps created
> with to_timestamp, everything is OK ("expected_result").
It is not "exactly the same arithmetic", because to_timestamp
delivers a result of type timestamp-with-time-zone, whereas your
other values are evidently timestamp without time zone. You did
not say what timezone setting you are using, but I think the
discrepancy is probably explained by that.
regards, tom lane