Manipulating SQLite Datetime objects?

I'm fairly new to SQLite, and am used to manipulating the datetime objects in Python, ala object.hour, etc...

I have a script that creates an initial SQLite DATETIME('now') time-stamp, and then I have a second script that I want to be able to return all rows that have a time-stamp more than a half-hour old.

My first attempt was to try:

SELECT DATETIME('now') - sent_to_pivot --my timestamp
FROM aud_qty

This was just to see if it would return anything, and it returned '0'.

When I replace DATETIME with TIME, it gives me '-1377'.