The latest I have seen a timing failure was on 06 LEO Explorer, which had about 150K plus idle time. This was in 2011 or 12, so lots of idle time.
By and large the timing chain tensioner issues were sorted out in production by 2005, so anything after 06 should be pretty safe.
The tensioners are the root cause of the failure though, and those by themselves are not expensive or hard to do, so cheap and easy insurance to replace them.
What happens is that the tensioners get weak, then they allow the chains to start wobbling and slapping the guides. The chain slap is what breaks the guide, and that is when you end up with issues.
I've also seen a few instances (one in person, a few others on-line) of the bolt that holds the rear gear on the jack shaft breaking. I'm not sure what causes that. It seems to be common enough that you can find stories if you look for them, but seems to be far from an abundant failure.
Despite all the boogey-man stories and guys saying they will never own one the 4.0 SOHC is a good engine that has very few problems. Even the timing chain issues wouldn't get near the hype they do if it wasn't such a pain to fix.