the night market moves around the island. In Kuah on Wednesdays and Saturdays. On Thursday in Pagan Matsirat. about the other days I am not sure.
It starts around 6ish and goes till about 9.30 I think.
Morning markets are mainly to buy fruits, veggies, fish and meat.
Panti Cenang markets are on a Thursday evening, starting around 5.00pm.
They are about a 20 minute walk from the restaurant/bar strip in Cenang. There are always lots of taxis there.
As Eva said they are basically for locals to buy fresh fruit and veg and some yummy local food.
Good to visit, but you can "sample and see" in around 1 hour, then head on into Cenang for the evening.
The operating hours for Kuah Town markets are as per Eva has already said. They are much larger than Cenang markets and in my opinion more to see.
It is a great place to call into if you plan on going to Tanjung Rhu . They are open 7 days a week from around 1000 to 1800