There's no timeframe for when to begin giving feedback, but a general rule of thumb before giving negative feedback is to get to know your new teammates and build a good understanding of their strengths and weaknesses first. If you become a manager in the middle of a project and notice challenges on the project due to the behavior of a colleague you haven't had the chance to get to know very well, do not delay the feedback. For more on this topic, read: Giving Feedback to New Teammates.