Windows 7 Explorer only shows the last modified time of files and folders in hours and minutes, not seconds, i.e. hh:mm instead of hh:mm:ss. If you use the Properties dialog, you can briefly see the last modified time in hh:mm:ss but if you wait longer, the text in the dialog changes to the pretty useless "n minutes ago" and then a more useless "m hours ago". If you check the file or folder properties the next day, you can see the last modified time in hh:mm:ss again! This misfeature became a problem when I wanted to check the modified time of files created seconds within each other.
The workaround is to change the Long date format in your Region and Language from dddd, d MMMM yyyy to ddd, d MMMM yyyy, which stops last modified date format from changing in the Properties dialog. Note that Windows 7 Explorer's Date Modified column never shows seconds.
Reference to self: use "HH:mm:ss" for 24-hour time format and "dd/MM/yyyy" to ensure that day of month always has two digits.