TimerAtTimerAt — attaches an event handler to an "at" timer.
TimerAt (day, month, year, hour, minute, second, fn)
dayRestriction on the day of the month
(1-31), or nil for none.
monthRestriction on the month of the year
(1-12), or nil for none.
yearRestriction on the year
(1994-2026), or nil for none.
hourRestriction on the hour of the day
(0-23), or nil for none.
minuteRestriction on the minute in the hour
(0-59), or nil for none.
secondRestriction on the second in the minute
(0-59), or nil for none.
fnA function or method call.
This method sets an at timer that causes the
fn function or method to execute at a specific time,
or to occur regularly at certain times of the minute, hour, day, month or year.
A restriction on a particular attribute of the time will cause the timer to fire
only if that restriction is true.
A restriction may be any number in the legal range of that attribute, or a
list of numbers in that range. Illegal values for the time will be normalized.
For example, a time specified as July 0, 2008 00:00:00 will
be treated as June 30, 2008 00:00:00. If nil is
specified for any attribute of the time, this implies no restriction and the
timer will fire cyclically at every legal value for that attribute.
This method also creates a unique, sequential ID number for the timer,
appends that number to the class's ._TimerIDs list, and
returns that same timer ID number.
Timers created using TimerAt, TimerAfter, and TimerEvery are
automatically cancelled when the Application instance is destroyed.