Let's try this:
Drop the format line completely from the xml definition. In its place try:
and see what that gives you.
My guess here is the system is ignoring the time section of your format string because you haven't told it that the calendar field should include a time (the showtime parameter). I also think the ...
Your %I should be %i, as per the php docs you are setting a boolean value (Whether or not the date is in daylight saving time - 1 if Daylight Saving Time, 0 otherwise) in the middle of the datestring. I assume you were probably looking for lowercase i, which is minutes with leading zeros.