Hi Mark
With the majority of mirrors I've made I have made the telescope at the same time so have been able to check the final correction by star test.
Particularly with plate glass when the scope is first taken outside the figure shows some undercorrection. The mirror and surrounding air inside the tube at this point is at ambient storage temperature so the undercorrected figure is what I have put on the glass (no worse than 1/4 wave). After a short time as everything starts to cool the correction increases. After another period the correction stabilises. I've found that the time of year (summer/winter) doesn't matter too much but sky condition does. If it's partly cloudy the correction won't increase as much as on a totally clear night. Obviously the important thing is the rate of temperature drop. In Hamilton the temp. difference between daytime high and nighttime low, on average (or on a typical day), is similar all year round. Off the top of my head around 12°.
I'm not talking huge amounts of correction change here but visible in the star test. I see the same thing in my 20" x 1.6" Pyrex mirrored dob.
I assume the Loftus mirror would behave similarly so if it passes through good correction in early cooling (sunset) I suggest a reduction in overall correction would be an improvement.
Did he say the mirror continued to gain correction the whole night or did the gain eventually stabilise?
If I'm figuring a mirror but not able to star test then I Foucault test in the early evening under falling temperature conditions. I test for smoothness under stable conditions though.
Incidently, loftus once ate his dinner off that same mirror.
Dave