First off, congratulations on the interview.

In my experience, the time for the interview depends on: 1) how many people you interview with; 2) questions you have; 3) how long it takes you and the interviewer to answer questions.

If you have not had a leadership position before, fret not. They probably know this as it is an internal position interview. But, try to speak to times you took initiative to problem solve, led a project or group (whether work, school, community, or other organization. Maybe even in you household.). Some of the questions might be, "how would you handle...", 'why do you think you would be a good fit for this position?' So, a lot of personality and management / supervisor questions. Just stick to what you know and your personality. Don't fib, better to not get the role and tell the truth, than get it by pretending to be something you are not. Typically, the real person comes out and it fails.

But, you note you are ready. That is a good sign. Confidence.

Best of luck and post back how it went.