Mini Cone Greenhouse update

Here is a bit of an update on the mini cone greenhouse.
[It was later found that the thermometers may have given inaccurate readings, so these readings are suspect. DD.]
I put a minimum/maximum thermometer inside the mini cone greenhouse yesterday. Overnight the temperature outside went down to -5.1 C in Yarmouth and there was frost here (I did not record the minimum outside here but I will tonight. In any event, there was ice and frost so it was 0 C or below outside. But inside the mini cone greenhouse the minimum temperature recorded was +11 C.

Also, the maximum reported temperature in Yarmouth (from http://www.weatheroffice.gc.ca/city/pages/ns-29_metric_e.html ) was +2.4 C
The maximum temperature inside the mini cone greenhouse was +22 C

This is encouraging, except now I need to worry about overheating on a warn sunny day. Removing the lid should prevent overheating as it could then vent out the top.
The conclusion is I could plant potato seed now and have local new potatoes to sell before others have them available.
Do you consider this significant?