Regardless of the specific rules implemented by a country, starting and stopping DST works the same way. A popular start time is 2 a.m., because most people are zonked out, and most businesses are closed. At that time, the clock moves forward exactly one hour. Here's a second-by-second account of what occurs:
1:59:58 -- it's standard time.
1:59:59 -- yep, still standard time.
3:00:00 -- we're on daylight saving time now.
3:00:01 -- daylight saving time rocks on for the next few months.
Notice that every second between 2:00:00 and 2:59:59 disappears completely. To start DST, a full hour must be skipped!
In the fall, when daylight saving time ends, you get the lost hour back because the time from 1:00:00 to 1:59:59 is repeated for one day. Here's what it looks like:
1:59:58 -- daylight saving time still rules.
1:59:59 -- DST's last hurrah.
1:00:00 -- standard time has assumed command.
1:00:01 -- standard time rolls on until the next time ...
Notice that the clock moves from 1:59:59 to 1:00:00, not 2:00:00. In other words, one full hour occurs twice, and the day ends up being 25 hours long. Most people don't ever need to refer to time within this hour, but if they do, say, because a birth or death occurred, they need to mention whether it was before or after the change back to standard time.
It's taken a few years -- and several changes -- to perfect this time-switching model. In the next section, we'll look at the history of daylight saving time to understand how it's evolved.