Time difference average between values in pivot table

Hi!

I'm trying to find the DIFFERENCE average between values in the same row in a pivot table:

For example:

A159:37
A1610:38
A1712:37
A1813:04
A1913:45
A2014:05
A2114:56
A2215:14
A2315:40
A2416:32
A2516:36
A2618:29
A2719:37
A2819:44

The simple formula for calculating this manually would be =AVERAGE(A16-A15,A17-A16,A18-A17,A19-A18…A28-A27)

The problem I have is that the data is in the first row (Row Labels) of a Pivot Table, which cannot be copied and pasted on the worksheet or workbook because the data on this pivot table will get larger everyday.

My closest approach to this problem has been the array formula: {=AVERAGE(OFFSET(A15:A27,1,)&-A15:A27)} which seems to be calculating what I need but for some reason returns the usual #VALUE! error.

I posted the solution (if calculated manually) on cell G4. Other cells have all the unsuccessful approaches I have taken.

Anyone that can help me with this?

Wow thanks a lot benishiryo! Worked like a charm!

Could you explain to me shortly how the height and width parameters affect the OFFSET formula? I have a fairly decent understanding of the formula but this part of it completely throws me off.

Thank you very much! You saved me a ton of work and head-scratching