Student or Learner
When you reply to a question, "What time do you get up?", which do you think sounds natural?
A: At six thirty.
B: Six thirty.
This may sound a very basic question, but I honestly don't know if it's acceptable to omit "at" here.
Both are just fine. I would probably not say "at."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.