Average Time Elapsed

In a table I have the time elapsed from received to completed in days, hours & minutes format. What would give me the average time elapsed for the entire column based on criteria. the criteria is

Formula:

Combined_Mailbox[Content.Categories]

The elapsed time is below. The criteria would equal a text value ="Name Here"

Formula:

=IFERROR(INT([@[Content.Flag Completed Date]]-[@[Content.Received]])&" days "&TEXT([@[Content.Flag Completed Date]]-[@[Content.Received]],"h"" hrs ""m"" mins"""),"")

I'm attempting to have the average time in the same format.

The average of the below column.

Formula:

Combined_Mailbox[Days Elasped]

In F2

=SUMPRODUCT(([Content.Categories]=[@[Content.Categories]])*([Content.Flag Completed Date]-[Content.Received]))/COUNTIF([Content.Categories],[@[Content.Categories]])