How long it will take to learn cycling for adults?

I understand that learning cycling can be an exciting and rewarding experience for adults, but I'm curious about the time commitment required. So, how long would you say it typically takes for an adult to learn how to ride a bicycle, considering factors such as prior experience, dedication to practice, and perhaps even any initial fear or anxiety that may come with the process? Are there any specific milestones or skills that learners should aim to achieve as they progress, and how can they gauge their own progress effectively?