The plot is always time_length long. For example, for a day plot, this defaults to 27 hours. The DST transition only affects the labeling.
Take this example from yesterday:
The total width is 27 realtime hours --- that doesn't change with DST. However, the advent of DST causes the major increments to the right of the DST transition to shift a little bit to the left --- if you will, we reached them quicker thanks to the "spring forward."
The density of data points across the graph remains the same --- one every 5 minutes --- but the labeling shifts around a bit.
As for the tallies: the March NOAA report starts with 1 March 2024 00:00, exclusive, and ends with 1 April 2024 00:00, inclusive. Those are local times. Because of DST, the table actually contains 1 hour less data than if DST had not happened.
Hope that helps.