Time Display Format
===================
The calendar and diary by default display times of day in the
conventional American style with the hours from 1 through 12, minutes,
and either `am' or `pm'. If you prefer the European style, also known
in the US as military, in which the hours go from 00 to 23, you can
alter the variable `calendar-time-display-form'. This variable is a
list of expressions that can involve the variables `12-hours',
`24-hours', and `minutes', which are all numbers in string form, and
`am-pm' and `time-zone', which are both alphabetic strings. The
default value of `calendar-time-display-form' is as follows:
(12-hours ":" minutes am-pm
(if time-zone " (") time-zone (if time-zone ")"))
Here is a value that provides European style times:
(24-hours ":" minutes
(if time-zone " (") time-zone (if time-zone ")"))