Since the Leopard (OS 10.5) upgrade, and until yesterday, I was quite reluctant to use iCal, for at least two reasons. Adding a new event no longer made appear the box of options, and second, it was time-consuming, after double or triple clicking on the entry, to figure out how best to input a start and end time in the box of options. For example, typing 14 in the hour field would instantly transform into 16. The up and down arrows were what I ended up using most of the time, because extending the event box with the mouse was not exactly accurate.
The reason is that I’m using custom time and date settings, a recipe that is just right for me (living in France and using English as work language) and that I spent a fair amount of time crafting and refining several years ago. I was loathe to have to touch it so as to compensate that fact that Apple had coupled iCal with input from international/regions preferences.
How easy the solution was: Open the System Preferences, look for International, select the Formats tab, look for the Times section, click on the “customize…” button, click on the hour and select “0-23” from the drop down menu. OK. Quit System Preferences. That is it.