valve lash

i know on bigger diesels (11 liter etc....semis) we got valves set every yr

i also know on duramax's they werent sposed to need re-doing as per owners manual, but some did adjust them to spec and got better results

anybody got the FSM for the ctd? does it mention valve lash/set anywhere...cant find anything on internet

im thinking timing belt service would be a good time for it?