Ed - once you leave the "At" setting (step 3E), it will read the box temp in the left window. It will get to 140 - I'll correct that in the instructions. Good catch! It should be flashing between "At" and the temp, to indicate it is autotuning.
As far as your second question - the only way to get temps higher than 250 are with the bypass. The autotune has nothing to do with how high the temp goes (seems the Auber will go up to 600°, if I'm not mistaken), but everything to do with how it gets there & remains constant there. This tuning adjusts those parameters for your box, so it learns how fast the temp climbs and falls, and how much power to add to maintain.