Postgres Intervals can be used with time as a way of determining a standard offset. For instance, I can concisely determine what the time was 2 hours earlier with
> select now() - '2 hours'::interval as earlier;
earlier
-------------------------------
2015-06-12 21:17:43.678822-05
or similarly
> select now() - interval '2 hours' as earlier;
earlier
-------------------------------
2015-06-12 21:17:43.678822-05