It's general concensus here that turbo timers aren't necessary on the TDI engine. Exhaust temps are quite a bit lower than on gas engines, and if you use a good synth oil then your turbo will be just fine. You might want to let it cool for 10-15 secs if you immediately stop after "spirited" driving, but otherwise it's no big deal.
Of the turbo problems reported here on the forum (VNT problems, grenaded turbos, oil leaks, etc etc etc) I don't think that any could be attributed to coking/lack of proper cooldown.