How often should I set Ads on YouTube videos?

Hi everyone. I have got a channel where are uploaded 10-11 minutes long videos. I have on every video ads in these time period: before video, 1:00, 3:00, 6:00, 9:00, after video. My earnings are low. CPM is 1 USD. Is it possible to change ads time period for every video in order to increase my YouTube earnings? What is the best time ads for YouTube video. I don't know what should I change in my YouTube Ads tactic to make more money than 1 USD for 1000 impressions now? Please, help me someone.

Best regards!

it may be that either your traffic is coming form 3 tier countries, or people are not viewing your video long enough for the ads to run, you can find out both from analytics in the creator studio

OK! Thanks for answer. I looked into YouTube Analytics and changed Ads time. Most people are watching videos (10-11 minutes long) through 5-6-7 minutes. So I changed Ads time and now it is: before video, 1:00, 2:30, 4:00, 6:00, 9:00, after video. More Ads in the beginning when people are watching videos. The audience of my videos is: 41% Poland, 17% Great Britain, 13% Germany, 7,6% United States, 3,5% Canada. In the beginning CPM was 1 USD and now is 2,6 USD. I wrote badly in previous post, cause I suggested old statistics. I would like to reach 3,00-3,50 USD CPM. Maybe it is possible. I will analyze videos and when CPM will not grow so I will change one more time Ads time. Thanks!