Date calculations give different results in different environments
sqlfiddle.com might interpret returned timestamps as having a timezone.
But PostgreSQL does not store a timezone along with a timestamp.
timestamp with timezone fields are internally stored in UTC: https://www.postgresql.org/docs/11/datatype-datetime.html#DATATYPE-TIMEZONES
A timezone is not returned in this query either.
So this behavior of sqlfiddle.com is misleading.