I guess that what this nets out to, is that if you log a "local time", you also need the time_zone.

I am in the US Pacific Time Zone (PST).
Once per year, a "day" will have 25 hours.
My wristwatch will wind up showing 1:15 AM twice during that day.
It is Ok that 1:15 AM PST and 1:15 AM PDST converts to a different GMT time,
but the time zone matters.

I recommend converting all times to GMT/UTC within the DB.