I put the Dutch oven into the oven before turning the oven on, so everything started cold together at 11:30. The main oven got to 500F at 12:10 (green line), and the inside of the Dutch oven got there a little later at 12:18 (yellow line), meeting the oven temperature as it was dropping back down after the heating elements cycled off. So I didn’t allow a lot of extra time for the Dutch oven to preheat separately.

I have read advice in some places that you should keep your oven at 500F for an hour or something to get the cast iron really hot, but at least in my case that doesn’t seem to be necessary.

I am curious about the inside of the Dutch oven remaining at about 350F for the first 20 minutes of the bake when the lid was on. I wonder if that indicates a fairly consistent rate of heat transfer into the bread. I did have the Dutch oven out of the oven for about 4 minutes while I was putting the dough into it. But after 12:24 the temperature inside Dutch oven doesn’t heat up again quickly like it did during the preheat.