First Assigned Time definition

First Assigned Time definition

Hello,
I'm trying to create a report in Analytics against Zoho Desk data, looking for the time difference between a ticket's creation time, and the first time an individual agent assumes ownership of the ticket (not the team).

I thought I'd use ticket create time, and "First Assigned Time", however first assigned time appears to change if the ticket exchanges ownership.

First response is not the measurement I'm looking for, as we'd like to know how quickly tickets are assigned.
Does anyone have any insight on what First Assigned Time actually represents, or which value I might use instead?

Thanks!