After adding all the insulation, I don't have a lot of data with the chamber in a steady state condition, then looking at the ramp.
In this picture, the box is configured the way it was prior to these new mods. There is a UNI-T UT181A inside the box and I am comparing various temps against what the box is reporting.
I would expect that the during the ramp, we have a heat start. With the smaller volume, it still takes 1200 seconds to ramp from 20 to 5C. But that meter is a bit of thermal mass. 20C to 0 was 2200 seconds.
Looking at the first part of the collection, you can see how slow the time constant is as the temperatures get lower.