I'd shoot for low 80s at your "basking site" (which is the branch/vine closest to the basking bulb) for a youngster. He likely will climb on the screen a good bit, which is part of why I'd say low 80s at the branch. Because right under the screen will be several degrees warmer.
Ideally the basking light should be at a angle with the light directed at a branch/vine that is a few inches (I'd say 6-10) below the uvb, this way while they are basking they're getting uvb.
I'm told they would typically bask in the morning and evening , so the "lateral basking" resulting from having the basking light at a angle is also more natural.