Here are some common answers to common questions

Q. What the heck is UTC?
A. UTC is Universal Time.  This is like Greenwich Mean time (GMT) except that
GMT time days officially start at noon in Greenwich, England.  UTC time is the 
time that your watch would say if you were in Greenwich, England.

Q. Does it take into consideration Daylight savings time?
A. No, you need to adjust for that.  Just add 1 hour to your
UTC  time in the summer. (Auckland becomes +13 instead of +12
and California becomes -7 instead of -8) 

Q. Why is the time the calendar says that the sun set so very wrong?
A. Probably because the location or Time zone is not set correct.

Q. Why doesn't the time zone get set when I choose a location?
A1. Because I am lazy. I figured most people could figure out their
time zone, but Latitude and Longitude would be a bit more of a stretch.
So, choosing a location sets the Latitude and Longitude but not the 
Zone.
A2. Because it is not always calculatable.  The time zone boundaries are
set up on political boundaries.  If it was straight off of latitude, that would be easy.

Q. Why don't you adjust for daylight savings time.
A. Because it is another arbitrary change.  The day that it happens can
an has changed.  Some locations do not recognize it.  So you are on your own.

Q. How do I find out what UTC to use?
A. You can go to the TimeZone Table and see what you UTC should be.