Total downtime for a list of nodes in a time period?

I would like to create a report to show a list of nodes and how long each has been down in a certain time period. I've seen some reports like this in THWACK, but they were created in the report writer, which has been deprecated and will be going away in the next release. I have tried creating one in the web-based version, but my report has downtime duration separated by each down event. I am looking to have a sum or total amount of downtime instead.

I'd also like to use some custom properties to only show my routers.