Peter,
I wonder if you can set the command to anything you want. Their example doesn't state that there are limits on accessing programs, such as '/usr/bin/wget', used by ListMail. Have you tried the ListMail default commandline as per the help at
http://listmailpro.com/help/dailymail_cron.html? The first part of the command "0 0 * * *" indicates the timing. Basically, we need to set the values of "Minute" and "Hour" so that the task runs once per day.
You may also be able to call the PHP script directly, without wget, but for that we need to know where the 'php' executable is. (It might be in your cgi-bin or home folder/bin). The command might then be similar to as follows (all on one line):
/home/sites/yourdomain.com/bin/php /home/sites/yourdomain.com/public_html/mail/dailymail.php?pw=YourPass
Your host should let you know the best way to set this up on their server. Let them know that you need to visit a web page automatically each day.
Regards