Will a CRON job be suitable for this?

Will a CRON job be suitable for this?

I have a database with an email address, an interval of how often someone
wants an email sent to them (ranges from every 5 minutes to every couple
of days) and the time at which an email was last sent. I currently have a
PHP script that runs through the database and finds times before the
current time and sends them an email and updates the time at which it is
scheduled send the new email (using the interval).
Would it be OK to set this script up as a CRON job and run it every say 4
minutes? Or would this create too much overhead? I have 500+ tuples of
data that it will need to traverse every 4 minutes.