Tire Flatspotting

[BoxMann]

I know what flatspotting is -- typical case of a car sitting for awhile, you get a bad shimmy-like feel, and then after driving a while it goes away as centrifugal force takes over and rounds out the tire.

My question is: can a tire flat spot in as little as 12 or 24 hours?

And a second question: does the age of the tire affect its tendency to flatspot and/or recover from a flatspot?

More facts: the Boxster S I just bought sat around for about 18 months before I bought it. Was only driven about 500 miles. Seemed like it took 100 miles of driving to get rid of the flatspot. But now, I find that even when the car sits for 12 or 24 or 48 hours, there is a classic vibration that happens at speeds in the 30's or 40's and goes away after 5 or 10 miles of driving. I never thought a flatspot could happen that quickly, but it exhibits the classic symptoms of a flatspot. Is that possible? The tires have excellent tread, but are almost 8 years old, no dry rot. Does the age of the tires allow it to flatspot quickly?

Any thoughts?