Why does datetime return repeated values?

When I execute the following code snippet in MATLAB

start_time = datetime('05-Nov-2017 00:00:00','TimeZone','America/Los_Angeles'); 
end_time = datetime('05-Nov-2017 03:00:00','TimeZone','America/Los_Angeles'); 
DateString = start_time:1/2/24:end_time;

This ought to result in 7 times: 00:00, 00:30, 1:00, 1:30, 2:00, 2:30, and 3:00 on the same day.

Instead, it results in 9 times: 00:00, 00:30, 1:00, 1:30, 1:00, 1:30, 2:00, 2:30, and 3:00 on the same day.

If I do the same thing for the previous day, Nov 4, 2017, everything is fine...

start_time = datetime('04-Nov-2017 00:00:00','TimeZone','America/Los_Angeles'); 
end_time = datetime('04-Nov-2017 03:00:00','TimeZone','America/Los_Angeles'); 
DateString = start_time:1/24:end_time;

Gives 1 x 4 datetime array: 04-Nov-2017 00:00:00 04-Nov-2017 01:00:00 04-Nov-2017 02:00:00 04-Nov-2017 03:00:00

How can I explain this behavior?

Answer 1

[MathWorks Support Team]

This is due to Daylight Saving Time (DST).

In 2017, for the United States, Daylight Saving Time (DST) ended on Sunday, November 5. Clocks were set back 1 hour to standard time from 02:00 (2 am) to 01:00 (1 am), local time on this day.

This leads to the repeated values, which is the expected behavior.