How do you say 6 O'clock in Japanese?

In romaji: Kesa roku-ji-han ni (watashi wa) okimashita.

In hiragana:　けさろくじはんに（わたしは）おきました。

In kanji:　今朝六時半に〔私は〕起きました。

The "watashi wa" is in parenthesis because, if the subject is already established as you or known to be you, you don't need to say it.