I am not an athlete but I play football. Approximately how many days will it require to learn a heel stretch? I want to be able to raise my leg up to head level so that the sole of my foot is facing the sky. It is a part of pre-fight yoga.
This is entirely dependent on your flexibility and muscle tension. Age also plays a factor as the younger you are the easier it is to stretch muscles out. You will have to stretch and test your flexibility to see how much progress you make before you can estimate.
No one can estimate your own personal flexibility as it differs with each person.