SQL query to retrieve conditional field value

I have a table of data (attached) which is a list of VisitID's with restraint orderdate, RenewalDate ,StopDate and DischDate.

I compute the interval in hours from the previous renewal order until the new renewal date until there is a stop order for each VisitID.

Sometimes the StopDate is not input.  What I want to do is show the interval from the last Renewal Date until the StopDate.  If there is not a Stop Date, then the interval will be from the Last RenewalDate until the DischDate.  If there is no DischDate then the interval is from the last RenewalDate until the Date & Time the query is processed.

How can I do this?

Thanks

Glen
Renewal-Stop.xlsx