Hey Thomas, I've had another look at this and managed to get something working.

Using the 'Support - Tickets' dataset, this is the custom metric I created:

IF ([Ticket status - Unsorted] != "Solved" AND [Ticket status - Unsorted] != "Closed") AND DATE_DIFF(NOW(), [Ticket updated - Timestamp], "nb_of_days") > 7 THEN [Ticket ID] ENDIF

I've called it 'Unsolved tickets - not updated in last 7 days'.

You can then add this metric to a report alongside the standard 'Unsolved tickets' metric and create a 'Result metric calculation':

COUNT(Unsolved tickets - not updated in last 7 days)/COUNT(Unsolved tickets)

To give you the percentage.

Is that what you're after?