I consider the ideal length for an individual coaching session to be about 90 minutes, but slightly shorter or longer periods are possible, depending on what the coachee would like to achieve in a session.
After an exploratory discussion, a cycle of a certain number of sessions is agreed with a week or two or more between them. That time is as important for the coachee as the coaching itself.
Many coachees, for example executives who are often on their own in solving issues or taking decisions, prefer to see their coach regularly,
e.g. once a month or once a quarter, with a possibility to schedule additional sessions as necessary.