Just learned it today! 😃
Make a textfile cronfile.txt:
15 /dir/to/php -q /home/me/test.php
Load the textfile into crontab:
$ crontab cronfile.txt
Confirm that the textfile was added with crontab -l:
$ crontab -l
DO NOT EDIT THIS FILE - edit the master and reinstall.
(cronfile.txt installed on Tue Jun 12 12:53:26 2001)
(Cron version -- $Id: crontab.c,v 2.13 1994/01/17 03:20:37 vixie Exp $)
15 /dir/to/php -q /home/me/test.php