How long can a baby slider turtle can be kept in sun?

I would say not very long at all. The baby turtle would cook in the sun. Why do you ask this question ?

In my opinion, turtles should always have immediate access to water. They will then move in and out of the water to the sun as often as they need. Don't keep the tank in the sun or you will get a build up of algae in the tank PLUS the water will get too hot and you will cook your turtle! I prefer to use a basking light. The basking area should be about 86 degrees F. Check the water temperature constantly to ensure it isn't too hot. A slider would need the air temperature of the room (thus the water would be about the same) around 75 degrees and the air/water temperature for a baby should be slightly warmer... about 82 to 85 degrees. Make sure your baby isn't too cold, otherwise it will get sick. Temperatures below 75 degrees with cause them to stop feeding properly and they can become quite ill with respiratory illness.

If it's a nice warm day I have a kiddie pool outside that I put a large rock in the centre for my red-eared slider. She goes out on warm sunny days. It's very important that they have a cooler area to retreat to when they feel overheated. I put water plants in the pool (and move them to the aquarium because she loves them not just for shade but for hiding and as a food source) and try to have one corner of it shaded with garden plants or a bush. DON'T use an aquarium for this as they get VERY hot in the sun.

My gal is about 12 years old (I've had her since she was a wee baby and she's HUGE now) and she's very happy and healthy, so it should be pretty good advice. :) Hope it helps!

Hugs, Didi