I would not suggest anything that relies on trains these days particularly travelling further than a potential taxi ride away . All aboard is usually around 4 30 so doesn’t give much time. Trains can be cancelled at short notice or not be as frequent.My advice from someone who lives in the area, is stay in Southampton. There is more than enough to see and do in the time available. If you really want to travel further afield take a Cunard excursion then you will be guaranteed to be back on time.