The sentences you came up with are all correct. There are a lot of ways to say that. It depends mainly on what the relationship between you and listner is. When you talk to your friend, です /desu/ sounds too polite. If I were to ask a friend of mine or my Mom or Dad what time it is now, I would say, simply, 「いま何時?」/ima nanji/. Then he or she would answer 「10時(だよ)」/juuzi dayo/ or something like that.
But if I were to ask my boss, teacher etc, I would ask 「いま何時ですか?」or 「いま何時でしょうか?」. If I were to answer to them, I would say 「10時です」.