I would use UTC date and time in ISO 8601 format timezone set to 0 in all timestamping operations given a choice. But we don't know where or how your data was collected. Here are the ideas use AbsoluteTime with TimeZone options, DateString can also make use of the time zone offsets which is good for plot labels to have the same ticks. For example:
Daylight Saving Time (United States) began Sunday, March 14, 2010, 2:00am, and ended Sunday, November 7, 2010, 2:00am. Except Arizona and Hawaii. Move your clocks ahead 1 hour in spring and back 1 hour in fall ("Spring forward, fall back").