Both structures are correct. But A = a question and B = the answer to the question A. So you can ask the question A like you suggest. And if asked the question A, you can respond with your answer B. PERSON A: "What time is best to visit the tourist spot?" PERSON B: "I think it's better to visit there at 7pm."

You can ask it either way, but I think "What is the best time..." sounds more natural.

Definitely you can. Either way is correct.