It handles whatever date format you have set in your Control Panel / Regional Settings.
In addition to that it always handles ISO format (YYYY-MM-DD hh:mm:ss). It also tries to "figure it out" in case of format that is neither set in control panel and it is not ISO. If it sees 1970/01/13 it is likely to figure it out that it is January 13, 1970. But in case of 1970/01/02 it is not clear if it is January 2nd or Feburary 1st.
So if you have a choice, use ISO format.