Applying summary level average for HHMMSS column

[Sakthi]

Hi,

I have a column [Resolution Time] which is calculated based on the two cols [Initiated Date Time] & [Response Date Time].
I'm extracting only time values from Initiated date time and response date time.
Also i need to apply average at the summary level for Response Time.
The problem here i'm facing is if i overall average for [Response Time] is only displays in days...
Can anybody help me out on how to apply average for HHMMSS at the summary level for the particular column.
Pls find attached example mockup.

Thank You..!!!