I agree with the previous chap, around 70k miles is right. If you're thinking of doing it yourself, think twice. The crankshaft pulley is NOT keyed to the crankshaft but only held on by a taper, so when you undo the nut holding it on, it is free to spin thus losing any timing marks you may have put on it.
Don't just replace the belt, do the tensioner at the same time as this was on the way out when I replaced it. Good luck Vince.
Vince, August 2010