As I bought a new thermostat, I did the same test today.
The results are similar. The new thermostat opens faster and a bit wider.
The difference is not so big like the one in the past which I believe has to do with the age of the 'old' thermostat which is only 2 years (and probably 10k km).
The new one on the left and the 'old' on the right.
Note the marking on the metal of the 'old' one, like if the tolerance is very tight.
The difference is aproximately 1mm (the new one opens wider).
Here right after I take them out, the difference is clearly visible.
I think the thermostat design has an issue.