it all depend on the person. if you have never done abny physical sports, it can take years before you reach a competitive level (level 4-senior elite). if you have done a physical sport, it might be...
If you are talking about learning the rules it does not take very long to figure it out. If you are talking about developing skill, it depends on the person.
It should take you about a week or so you have to learn kickflip or you wont be able to do any other kickflip like varial kickflip tre flip and nightmare flip