Idling at 200C is probably only drawing something like 3 watts on a T15 iron. And you can probably leave a Hakko tip at 200 C for weeks without touching it, with no ill effect. I think heat cycling might cause more stress to the internals than the worry over oxidation at relatively low temps.
If I could set both, I would have the auto power down at like 3 hours, maybe. 30 min is hardly time to read a datasheet while figuring out what the heck I'm doing.
I regularly leave my 888 on when leaving the building to go eat or something. At soldering temp. I have replaced only one tip in 9 years, and on further examination that tip is fine, too. (The iron sleeve on the inside broke loose, but it looks like it's just a press fit extra shim/doodad to begin with, put in there to protect the chrome plating on the "real" iron layer from wear when inserting/removing the tip. The creamy copper filling is still perfectly sealed and intact.)
Hope you get your answer from someone with this station. Sorry for the sidetrack.