I learned the ollie in about 3 weeks and was able to start ollieing over physical objects at around a month and a half. For me, it took about a year, because the board I had didn't have very much pop, and it took all my strength to even get the board 3 in. off the ground.
How do you ollie in 4 minutes?
https://www.youtube.com/watch?v=KJnZvKwgZaA
How do I train my ollies?
https://www.youtube.com/watch?v=Q0QR1eetkJ8
How long should I practice ollies?
It took me about a week of practicing to get the movements down and Ollie but just keep practicing and you will get better over time. For me it only took a coyple of days but other peoples average might be aslong as a month or as short as a week.