IF you're timing belt broke at, say, 70,000 miles and you had no proof that it had been replaced, you would be SOL. Not replacing it at 60,000 miles does not 'void' your warranty. But if your engine craps out and it can even remotely be blamed on failure to maintain the vehicle to the letter, I would imagine that is the road the dealer would take.

If, say, your engine overheated and warped a head, you might be denied warranty service if you failed to have the coolant replaced/recycled per your maintenance schedule. But they couldn't deny a warranty claim on a tranmission problem because you didn't change the coolant out. And if you change your timing belt at 70k miles instead of 60k, your warranty is not voided provided no problems associated with a timing belt developed between 60k and 70k miles.

Same as with changing the oil late... although it would be fairly easy for the dealer to assume that a related problem developed BECAUSE you didn't change the oil when you were supposed to.

As for the $1,000 to change the timing belt, find someone else (it doesn't HAVE to be a Hyundai dealership, although this goes a long way toward getting any warranty claims completed through them). A 60k mile service at my dealership runs about $700, and this includes the belt change.