When I had my last channel, YouTube used to let me manually insert ads in videos over 10 minutes long. Now, it only lets me turn "Monetize ads" on and off. Example: If a video was 13 minutes long, I could insert ads at 1:02, 3:10, 5:39, 7:11, 9:00, 10:50, and 12:00 for example. I can't do that anymore for whatever reason. I have over 10,000 channel views, but currently less than 100 subscribers.