Jets on LCY-EDI are apparently scheduled at 1h20min and the Dornier 328 on LCY-DND mostly at 1h35min or 1h40min. With a Fokker 50 on DND-LCY, we would be looking at up to 2h block-time. 40 minutes time difference is about half the driving time from Dundee to EDI (although of course parking/checking in at EDI will not be as quick as at DND)