A really nice trip, especially if you buy the all inclusive version drinks are available all the time on the boat and you get your lunch when you arrive at Comino.
The sail began at 11:00 starting in Buggiba, you go to Gozo to drop people off, then you go to Comino and arrive at about 12:30-12:45. You leave at 16:00 and at about 17:00 you are back in Buggiba.
Just be sure to take your stuff with you when you get off the boat, because the boat leaves for about 30 minutes to get people back from Gozo.
The Blue Lagoon is beautiful, but in high season it's so crowded it's unbelievable - you might have some trouble to find a place to leave your towel. That is the only disadvantage I think. More