I would interpret this as meaning 00:00 on Sunday, not because the statement has that meaning unambiguously, but because the alternative interpretation (24:00 on Sunday) would start/end DST during the night prior to a workday, something that's generally avoided. -----Original Message----- In the original post which prompted me start this string of discussion, Oscar van Vlijmen quotes:

DST starts on Sunday, April 30, 2006 at 12:00 Midnight local standard time DST ends on Sunday, October 1, 2006 at 12:00 Midnight local daylight time

To me, this is ambiguous. I cannot tell whether those references to midnight mean the midnight which occurs before 12:01 a.m. on Sunday, or the midnight which occurs after 11:59 p.m. on Sunday.