Hi Alan, Paleo can be done easily in a day. Though we did have a larger engine than the 10hp one.
Two years ago we used Thomas boat hire from the beach, he has a very comfortable ( leather seats ) speedboat. We had it for the day and managed a trip over between the islands, stopped at St Georges for lunch and went down to paleo.
The sea can be choppy at san stef, but once out the bay and round the headland can then be calm. Thomas will be honest with you about the sea conditions, I think it was the third day we finally got out so plan it early to give you time to reschedule if necessary owing to sea conditions.
It was a great day out and highly recommended, would suggest checking prices between San Stef travel and Thomas. Check whether fuel is included, if not allow for this, high fuel costs make a difference.
Regards Brian