A couple things about this...
1. Nicodemus was a Pharisee, but not just a Pharisee, but a member of the ruling council. He had been trained from childhood to be a leader. He was a very smart and learned man. He wasn’t your garden variety fisherman or farmer. He wasn’t easily duped or convinced by anyone.
2. He wanted to do the right thing, but sometimes, even good people will do the wrong thing. We all know people who are “good” but don’t know Jesus. Being good wasn’t the issue. It was did he know Jesus. He chose to eventually leave the Pharisees and follow Jesus. Sometimes we are not able to change the people or situations around us and we are forced to make a choice. It probably was a hard choice for him, but he made it anyways.
3. He came at night. Two possibilities here...
a. One, both were busy men and Nicodemus both respected Jesus’ time as well as his own responsibilities. He took time out of his schedule to meet with Jesus.
b. Two, he was afraid of what others in his circle of friends would think. But it wasn’t that he was afraid, but the main point is he conquered that fear and he DID meet with him.
4. He tells Jesus things that he has heard and seen in others.