How long does it take to take control of all seven chakras in our body?
The length of time it takes to take control of all the chakras is the same amount of time it will take for each of us to reach final liberation and oneness with God. For some it will be quickly, for others, it may take many lifetimes.
The good news is that it is inevitable; it is our eventual destiny — we have no other!
The other good news is that there are ways to "shortcut" what might take a very long time. Paramhansa Yogananda describes this in his Autobiography of a Yogi in chapter 26, called "The Science of Kriya Yoga. In this he explains that by faithfully practicing the Kriya Yoga meditation techniques that he taught, final liberation is achievable much more quickly, than by simply living the best sort of life that you can and hoping for the best.
If you feel attracted to Paramhansa Yogananda and the path of Kriya Yoga, it would be our great joy to help you learn the Kriya techniques and to prepare yourself for Kriya Yoga initiation.
In the meantime there are many ways to gain a deeper awareness of the seven chakras and to learn to awaken and purify them. You might want to read my book Chakras for Starters or listen to my audio CD of the same name, both available through Crystal Clarity Publishers.
Many blessings and joy to you!