I set the oven to its maximum temperature of 220C, then turned on the fan and both the top and bottom elements (this is called the "bake" setting on my oven)

I have made the original spreadsheet available for download. Temperature was measured using a K-type thermocouple attached to my multimeter and logged every 10s. The oven was turned off after 20 minutes, and the door opened and left ajar at 30 minutes.

While heating, the temperature increases by a maximum of 1 degree per second. This is usable, but faster heating would be desirable. An easy way to improve the performance will be to add some insulation to the heating chamber.