According to the introduction of pet circle network, tadpoles can bask in the sun for about 1 hour, and it's nothing to bask in for a while, but it's best not to bask in it for too long, because tadpoles like to grow in dark and quiet places, such as places with strong sunshine, which can be partially sheltered.
Suitable containers for tadpoles are: large aquarium, large ceramic baking utensils, outdoor small pool, bathtub, laying suitable "foundation" for tadpoles' houses, etc.