The biggest floating market in the Mekong Delta is called Phung Hiep. Markets open at 5 am and are open till 11 am. This is one of the reasons I recommend a stay of at least two days. The only way to visit one of these floating markets is staying in the Mekong Delta area, waking up early and taking one of the boats first hour in the morning. The Delta is too far from Saigon to visit one of the markets if you do not sleep here. If you do a one day excursion, you will only see the canals. Markets will be already closed by the time you get here.