I calculated a 13:30 arrival local time, departure time is 17:00, hardly time for an excursion
Iona has head winds for some of the journey so it won't reach maximum speed
635 miles to Stavanger, at full speed (21 knots) it would take around 30-31 hours
At an average of 19 knots this journey would take around 34 hours plus a bit extra for weaving around traffic