I’m trying to do a “time to convert” funnel analysis which looks at the duration between the first instance of an event and the last instance of an event. 

This is kind of a proxy for session duration, or dwell time, but it’s more flexible for our use case because it can span multiple sessions (as they’re defined by Amplitude). 

When I try to do this as a funnel showing time to convert, it just gives me the time to convert between the First event and the next instance of that event. 

How can I calculate the time between the First and Last occurrence of that event, with an unknown number of other events (including that same event) happening between those two bookends? 
 

More examples: 

Here, in between the first and last event, any number of events could happen, including more of the same, for an undetermined amount of time. 

For this case, the correct answer to “time to convert” should be roughly 2 hours 16 minutes (not 2 minutes, because that is the next instance of this event.