There should be a way to put a device(s) under maintenance, after the maintenance actually happens. There are cases when technicians are missing to unmanage the device(s), or create a downtime through the Downtime Scheduler. Some authorized admins should be able to create the maintenance afterwards, which would affect past records. At the moment, the down time is not adjusted if you create this downtime scheduler after the downtime actually happens.

Anyway it is doable currently? 

Regards