Ferber method/ cry it out

My 9 month old can only fall asleep whilst nursing and I cannot put him down otherwise he is awake again. Tonight we’ve tried to put him in his crib a basically let him cry it out. It was very difficult for me but I’m so tired. I don’t have any time for myself because during the day he naps on my lap. He cried for nearly 90 minutes. He was standing up in his crib. After 90 minutes i took him out of his crib and he fell asleep on me straight away. How long do you mums let your baby cry it out for? Am I doing something wrong?