How long until Earth was habitable?

Could you please clarify for me, what exactly do you mean by "habitable" in relation to Earth? Are you asking about the point in Earth's history when it first became capable of sustaining life as we understand it today, or are you referring to a specific set of conditions that would make it suitable for human habitation? Additionally, is there a specific aspect of Earth's habitability that you're interested in, such as the development of an oxygen-rich atmosphere or the presence of liquid water on the surface? With this understanding, we can then delve into the scientific evidence and theories that may provide an answer to your question.