Hey,
AS 3.0 is powerful. Get your basics strong, and you'll be able to code games with real ease. However coding is just one part of making a flash game. You have to cover artwork as well for an appealing game experience, no one like playing with boxes and circles (Didn't get that? well you will once you get into this thing
)
As the question still remains well I can't say for sure but 3-4months of pure dedication is the least I can say. You said you can give it 5 hours a week, then let me tell you better quit while you are ahead. If you say 3-4 hours per day, then we'll talk about game making.
Its not as easy as it looks, there are tons of things going around in a flash game. Not discouraging you just informing you. Time is the only factor due to which I don't make flash games anymore.