We were in Athens in April. we booked HP tours find them on trip advisor. They picked us up from the hotel, which I might add changed middle of the night, that's another story, anyway I sent an email at 2am to say we had changed hotels, and we were delighted when Frank arrived.
we did a half day 8.30am until about 2pm, he then took us to the ship.
We saw as many sights he could pack in, the tour doesn't include entry, but it's not hugely expensive for entrance. our luggage was safe as Frank stays with minibus. Cannot recommend highly enough, and they will do it the other way around, pick you up after you disembark.