set the 'event' type as the default calendar form :
create a custom form: tools / forms / design a form....
choose all day events for time setting.
publish the form: tools / forms / publish form as...
assign the custom form to the calendar: navigate to properties on calendar folder, choose the new "event" type in the drop down for the default.
if needed, delete the form by selecting properties for the folder, upper tab "Forms", then 'manage...' (button).
eh, ymmv.
Outlook Calendar Start Time Shortcuts
One of the best undocumented features of Microsoft Outlook - well, undocumented as I can tell - is the "calendar shortcuts" feature. When you create a new appointment or task, you don't need to know the exact date of the appointment or task - let Outlook figure that out for you!
For example, if your boss tells you that a particular report is due in 25 days, you don't have to manually figure out when that is - just enter 25d in the "Start Time" for the appointment (make sure that today is selected in your calendar, otherwise the appointment will be added 25 days from the day selected).
Other available operators include W (weeks), MO (months) and Y (years) as well as TODAY, TOMORROW and NEXT TUESDAY (or whatever other day you need next week). Note that these calendar shortcuts also work with Tasks as well.