It really depends for me. I usually experience depression from late August until Marchish, so that is 6-7 months? But it varies in severity over that period. Hypo/mania varies a lot more. Everywhere from a few days to a few months. 2-3ish weeks is typical.

When I was 14, I was hypomanic for a good year, haha. Also had a super long hypo period when I was 17. Before I was dx'd bipolar and knew what was going on, I called the first period the "era of light" because I really felt that I really grew as a person during that time. I've been trying to achieve that same, stable sense of productivity and positive mood ever since...but it's never come back that mild and long since.