My side neck turtle didn't use the basking area for about a month after I got her, but now she does so regularly, on a daily basis. It may be that the turtle needs time to adapt, but I'm no expert.
We have a Cumberland slider. I didn't see him bask for weeks, because he was skittish and would only do so when no one was around. They know when they need to dry out, he may be going up there at night? Have you tried placing him under the heat lamp?
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