The life of air filters varies widely by type and where you operate your bike. Here in Tennessee, my filters require very little attention, but when I lived in dusty Albuquerque, NM I had to check them often. It's best to stick to the recommendations in the manual until you start to see trends emerge on your particular bike.
And uh, exercise caution when removing the stock filter. The thing is build like a cheese grater and there is very little clearance from a frame tube that is basically in the way of removal. You'll scratch the heck out of the frame if you just yank the filter out. (solution - a thin cardboard protector over the frame as you pull the filter.)
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