Ok, I didn't find an easy way to do it, but I did get it working with just a MySQL query. For future reference here it is. Note that I want the average from a set of data, so if you wanted the difference of a single date, you would skip the Sum(), Count() and Group By aggregate functions.
SELECT FORMAT((((SUM(UNIX_TIMESTAMP(DateLastUpdated))-
SUM(UNIX_TIMESTAMP(t1.DateOpened)))/86400)/COUNT(*)),0) as DaysOpen,
FROM tblTickets WHERE
DateLastUpdated>'$StartRangeDate' AND DateLastUpdated<'$EndRangeDate' AND StateId='12' GROUP BY PriorityId
Basically, I am getting the unix timestamp for the two dates, then I subtract them, leaving me with the time difference in seconds. Then I divide that number by 86400, which is the number of seconds in a day, which give me the number of days. Then I divide by the number of results I had, since the days returned, was the sum of all results. Then I format it to remove any fractions of days.
If anyone knows of a cleaner way, I'd love to hear it.
