∼20 years
Charles Darwin took approximately 20 years to present his ideas to the world. He developed his evolution theory through natural selection during a voyage that ended in 1836. However, he did not publish his ideas until 1859.
Before presenting them to the scientific community, he wanted to ensure that his ideas were accurate and well-supported. Additionally, Darwin was aware that his ideas would be controversial, so he may have wanted extra time to prepare for criticism. In 1858, Alfred Russel Wallace sent a letter containing a similar natural selection theory, prompting Darwin to publish his ideas.