There is no one answer to this question. There is no industry accepted/standard "tune up". Every bike has it's own issues and areas of greater or lesser needs. Yesterday's work showed this quite well. I did tune ups on two bikes with vastly different job times, note neither job was (or could be) done without distractions, other shop responsibilities and such.
The first job was on a few years old hybrid (Trek FX2) that saw frequent use. The bike was covered in salt and grime, worn chain and brake pads, upper der pivot (B knuckle) frozen tight and the usual wear and tear of a bike that isn't well cared for but used nearly daily. this job took about 4ish hours. Granted it's scope was beyond the usual tune up (and we did charge extra) the service writer didn't pick up on the bad pads and der pivot not working, but this missing condition during the assessment at drop off is fairly common even though we do a good job at service write ups (better then most shops do). Now during this time I took in a few more repairs and had half my lunch (the other half never got eaten
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Job two was a 3 year old Terry in really nice condition. Clean and no wear or other issues. This job took about 1 hour and that time also included a few service write ups (it was the end of the day, customers were getting out of their work).
Every shop I have worked in has had their version of various jobs they called "tune ups". Some only allow for barrel adjustments, don't drop wheels or pull freewheels to access hub bearings, don't clean or wipe off the bike and don't test ride after (or before the work, if called for). Other shops followed the Barnett School guidelines, have included a pre and post test ride, the post service test done by an other person to avoid self delusion. There's a BIG difference, a HUGE range of actual expectations from the boss (as well as the customers, I've found cheap prices generally collect low expectations).
Some within our industry has tried before to create some common standards. The Barnett's Service Manual was the best example of this (from the mid/late 1980s). Currently there's a movement to establish certifications for wrenches which will include some standard job expectations. Andy (who's desk top computer is in it's repair shop and this is the first lap topped posting done since. he hates the lap top keyboard/pad and was trying to not log in on this different computer but this thread called out for some reality).