General :: Using Datediff In Non-normalized Database

I have a SharePoint list that tracks the date/time of each stop of an order from its origin to its destination. The number of stops varies depending on the type of order (you can use train as a metaphor). The goal is to calculate the average time between each stop (we're trying to figure out where orders typically get held up).

Let's say there are stops A, B, C, D, and E. Every order starts at A and ends at E. If they all made every stop, I could easily get the average of datediff("d", B, A) etc.

However, since they make different numbers of stops, what I need is the difference between the stop and the last stop they actually made. I need a crosstab query (or report) that lists the OrderType as the row, the StopName as the column, and the average(datediff) as the value.

In a perfect world, this would be normalized and I'd have separate tables for the stops and the order types, but trying to do that through SharePoint is Not Fun and is going to confuse the end users.