I hate the biannual time change.

Okay, I had to get that out of the way. Anyway.

The magic that controls what your local wallclock time (assuming your system clock is on UTC) resides in a compiled ruleset which is described by /etc/localtime. On a Debian system this a symlink to the actual timezone file, which is in /usr/share/zoneinfo. On some other systems the file is actually copied, not symlinked. The result is the same, though.

What if you want to actually see what the ruleset is for your timezone? Check out the Sources for Time Zone and Daylight Saving Time Data. From there, you can download a copy of the uncompiled zoneinfo rules and examine the one for your locale. Therein you’ll find, at least for the North American zone, some interesting comments along with the actual rules. The ZIC(8) man page has details on how to interpret the rules within. Where applicable, the DST offsets are included.