Timing set interval

I have a '99 Malibu with the 3.1 L and haven't been able to find what GM recommends as the interval to change the timing set. It's at 130 K now. Does anybody know when they recommend this or is this now one of those things GM claims never needs changing (I know at least the 2000 and up V8s don't have a timing set recommended change point according to a GM rep.)

This is not a maintenance item, if you are worried about wear, get a wrench on the crank pulley and rotate the engine slightly in opposite directions and you will feel how loose the chain is, mine at 175 k was neglible