The distance from the Cooper Island anchorage to the middle of Soper's hole is 13 miles. The direction is pretty much downwind and since charter boats don't have downwind sails the speed won't be great. Motorsailing you could be doing perhaps 8 knots. So calculate 2 hours including picking up a mooring in Soper's hole.

Addendum - I just realized that you were returning your boat to Voyage charters in Soper's hole. I assume that they have a protocol, perhaps including a diver, for returning boats and this could take a while. There's a chance that they might not open early enough or that someone is ahead of you in line, so I would check with them first to see if you can make your 9am private ferry.