Recently bought a TL ES (manual of course) and the standard stereo is CRAP! I want to fit a reasonable head unit but my wife likes the feature where you can remove the key but still run the stereo for a while.
Does this feature still work with an aftermarket headunit?

Purely a function of the Head-Unit. Some base-model TJ's had a single-cd HU with a "one hour sleep" function which ran radio or CD without need of the ignition key. I liked it, too. Its possible that some after-market HUs have similar feature, but you'd have to shop-around.

Bugger! I was hoping this might have been a BCU controlled-feature as opposed to a feature of the HU itself. Thanks for the quick response Elwyn.

blaupunkt has that feature.... but im not sold on modern blaupunkt (read philips) gear