The cron "system" usually includes an at(1) command.
Example:
Code:
$ echo sh bin/script | at 1am tomorrow
commands will be executed using /bin/ksh
job 1240290000.c at Tue Apr 21 01:00:00 2009
$
edit:
You can also use "now +" -- specific to your needs:
$ echo rm /path/to/file | at now + 48 hours