The RX 350 has a Timing chain, not a belt. (The 330 had a belt). With proper care and maintenance on your engine, it should last a long long time... but I would plan to replace @ 150,000. It will eventually wear out..
The 3.5 liter V6 engine in a 2007 Lexus RX350 has a timing CHAIN
chain i work at engine rebuilding company we are doin one as we speak
In 2010 Lexus RX350's started using Timing Chain's in the 3.5 engine, which require no maintenance (unless very high mileage is reached or parts failure). Earlier years <2009 had timing belts. I verified the 2010 model has a timing chain via contacting a local Lexus parts department.
The 2008 Lexus IS250 uses the 4GR-FSE Toyota V6 engine, which has a timing chain.
The 1991 Lexus ls400 has a timing belt.
There is a timing belt on the Lexus ES300 2003.
Timing belt.
How much is a timing belt
timing belt
The 3.0 litre V6 engine in a 2000 Lexus ES300 has a timing BELT
Lexus manufacturer recommend replace timing belt on Lexus rx300 every 105,000 miles.
The 3.0 liter V6 engine in a 2000 Lexus es300 has a timing BELT