After watching Scotty for the last several years, I'm pretty sure his answer would be, "It has a timing chain, not a belt.  So, it should never need replacing as long regular normal maintenance has been the norm for this vehicle."  As for myself, I just bought a 2011 RX350 (based on Scotty's recommendations) and the last thing I'm worried about is the timing chain.  Mine had 72K when I got it, so I'm contemplating changing the  transmission fluid and the coolant since i don't know what's happened before I got it last month. Then I can be sure it has all the "Right Stuff" that it should have going forward.      

If you ever lose your timing chain on that car, you're the unluckiest guy in the world.

Change the engine oil and filter every 5000 miles and you won't have issues with the timing chain especially with that beast.