This is activated whenever the real-time clock is equal to the time specification you gave it. The time specifications should be one of two forms:
HH:MM[AM|PM] where 1<=HH<=12 and 0<=MM<=59
HH:MM where 0<=HH<=23 and 0<=MM<=59
which form you use depends on the current setting of
CLOCK_24HOUR. Time specification may include wildcards as
well. The matching of the real-time clock and the time
specification is a pure textual match. Of course, wildcards
may be used in the time specification.
The parameters for the action are as follows:
$0 The time (format depends on CLOCK_24HOUR variable)
See Also: set/clock_24hour