when to change deck belt

[eastportstar]

just wondering when is the time to change the deck belt on my 2010 zmaster 48. it's got 350 hours on it, was gonna pick up a belt just to have as a spare but they're almost $100. no indication of problem yet, but never had a ztr before this one (i bought it new). so far i've only changed the filters and oils. it's been a great machine. also, how many hours are you guys getting out of blades. i'm on my 5th set of blades so i guess they're lasting 90 hours per set (sharpened maybe 4 times, now they're all shot).