Formal:
* Je me suis réveillé à six heures. (Male)
* Je me suis réveillée à six heures. (Female)
Informal:
* Je me suis réveillé à 6h. (Male)
* Je me suis réveillée à 6h. (Female)
* J'ai dormi jusqu'à 6h. (I slept until 6)
* J'étais réveillé à 6h. (I was awake at 6)
Important Note:
* "Se réveiller" means "to wake up". It is a reflexive verb, so you need to use the reflexive pronoun "me" or "se".
* "À six heures" means "at six o'clock".
* "6h" is a more informal way of saying "six o'clock", and is commonly used in spoken French.
You can choose the best option based on the specific situation and who you are talking to.