Sounds kind of similar to the IncidentDurationByDays report as described by Lara in this post http://community.landesk.com/support/docs/DOC-5420. This takes into account clock stopped time.
If so, then it might be a good start to take a copy of this report and then modify it to suit your requirement? Only later versions of the product will include this report on the CD and its a good idea to get the latest copy of the report as there have been improvements made more recently. You can request a copy off your support team. It hasn't been tested against all older versions of the product but it may well work.