Hi Ronit, sorry for the delay.

ISO8601 has several acceptable representations for (human readable) times. It does use a 24 hour clock and requires zero-padded values (e.g. 8am is 08:00:00). Both of the human readable formats you list above are acceptable ISO8601 formats, so I'm not exactly sure what you are asking. As far as internet standards go, ISO8601 is implemented via RFC3339 , and this also true for iOS.

Perhaps if you could provide a little more insight into what you are trying to accomplish, I could provide a little more direction. If you are dealing just with times, I find it's easies to turn everything into "total seconds" do all my calculations using that value, and then only convert back into some human readable time at the end (for display). In this case, I don't actually use a "date" object.