production=# show timezone;
TimeZone
----------
UTC
(1 row)
production=# select ' 2011-01-01 00:00:03.925-06'::timestamptz < '2011-01-01'::date;
?column?
----------
f
What Tom said - though I missed the part about "the timezone when the data was entered" - I was thinking it was only the timezone at the time of the dump that would impact things.
To your example - testing in UTC is going to always result in failure for Z values <= 0 since they will all result in a UTC date of 2011-01-01. Choosing +06 would result in a passed test.
David J.