Well if it's a aquatic turtle they can stay out of water all day with no problems!!! I know that because I have a Red Eared Slider...
Indefinitely. It does need to drink, however.
They need a land and water area provided we have the same type of turtle in mind (usually meaning yellow bellied slider) and they are an aquatic turtle (aquatic implies water, lol). They must have water as a drinking source and aquatic turtles also need water to eat (and babies must eat daily) so without it they would starve to death as well. An improper environment (and diet) kills a turtle VERY quickly. Here's some great resources for you.
I left my slider turtles to play in the garden yesterday went back 20 min later and they are no where to be found how long can they survive and how far would they go from the yard?
We just got our turtle for easter and he was active for a few days and now seems to out of the water more and sleeps more. It eats a little. What should we expect from his habits?