Is it possible to report on next and subsequent reply time in Insights?
Next and subsequent reply time are not possible to track in Insights and therefore prebuilt metrics for it do not exist.
Zendesk calculates first reply and full resolution times, but does not calculate ongoing reply times. Insights can get the first or last reply time (using SELECT MIN and SELECT MAX), but it is not possible to find the third reply, and so on.
However, a workaround option is to create an SLA policy with a next reply time target for your tickets. For details, see Defining and using SLA policies (Professional and Enterprise).You can then report on the amount time the target was active on a ticket.