It's probably neither (and both). But what is the standard, if any, if one is writing a contract? If I want something to expire on midnight between March 11 and March 12, how is it defined?
0h00 2009-03-12 ?
24h00 2009-03-11 ?
0h00 2009-03-12 ?
24h00 2009-03-11 ?