whenits [-d] {time} {/path/to/command {arg1 arg2 arg3 ...} }
-d ... optional: daemonize (fork and run in
background). You'll need this if you're
scheduling commands that need to run after
the current shell closes.
time ... Required. Execution time may be specified
in absolute epoch seconds, or relative to
current time - eg now+5s, now+10m, now+2h.
command ... the command to be scheduled at {time},
along with any arguments to be passed to it.
(because at is only granular to 1m, wtf?)