This document is an excerpt from the Visualizing PI System Data Workbook v2017
The short answer is, it doesn’t!
When Data Archive collects data it converts the time to UTC (Universal Coordinated Time), or what used to be called Greenwich Mean Time (GMT). This means that each day has exactly 24 hours. The local machine clock of the user looking at the data makes any adjustments for time, such as time zone or Daylight Saving Time (DST).
So once a year the day will look like it has 23 hours and another 25, but the Data Archive never knows anything other than 24-hour days.
Also, because the clients and Data Archive know what time zone they are in, the data can be viewed in either Server Time or Client Time. This is determined by a setting in the client tool.