Hope fully this is an easy fix, and I've just missed a setting.
I have my time format on the Cosmo set to 24 hour, and in Agenda it displays correctly in lists of appointments. However in the create/edit entry dialog, it is insisting on using 12 hour dates. To make matters worse, the AM/PM selector appears to be a screen only control, and doesn't seem to accept keyboard input (at least the obvious option of pressing "A" or "P" to select it doesn't work for me.
Hopefully there's a way of setting it to 24 hour date entry. Forcing everyone to use 12 hour dates would seem a major omission, especially since I believe 12 hour dates are fairly alien to one of PC's major markers, Japan.