For me it says one and a half hour longer... And from having tried both routes (not in a MS though) that seems about right. Unless you have to wait really long for the ferry. Of the 300 km from hamburg SC to køge SC, 19 km is a ferry so it's more like 285...
I tried both roads (not Tesla) and the way over Fehmarn (A1) is really 1.5 hours faster (without the extra SuperCharging-Time on the longer other route!!)