Hi There

Thank you so much!! :)
To be honest I'm not sure how long in terms of time, maybe a year? It's always ongoing - regardless of which point you are at, you can always study and experiment with light and maximise your images.
My suggestion is take photos in :

Full Sun
Full Shade
Sun at different angles
Sun with a reflector (various sides) and various angles

Get a model and take photos in the sun at point a, and then make your way around them (360 degrees) and take photos of them (make them turn with you) - that way you will really start to understand natural light, and the impact it has on the subject.

The more you do it the more you'll understand it, and you'll start to know how certain light will affect a subject just by looking at it - also, look at the shadows on the floor (how defined they are) as that's an indication of how harsh the sun is too.

Different times of the day also affect your subject of course, so do some shoots in the morning vs midday vs evening :)

That's a massive list but I hope that helps