I have routinely started my Challah below 400 degrees and baked about 30 - 40 minutes until internal temp. reached a minimum of 180 degrees. Tried an experiment yesterday with good results; thought I'd share the details.
Preheated oven to 550 degrees with stone on middle rack. Used parchment paper to load the braided loaf onto the stone, closed the oven and baked five minutes. Then, opened the oven door to second notch, reduced heat to 350, and allowed the oven to cool as the bread continued to bake. When the actual oven temperature reached 350, closed the oven and finished baking to about 190 degrees internal temp. (came up to temp. in shorter time than expected). Cooled on rack one hour before slicing.
Results: Amazing oven spring, pefect browning, nice open crumb. I'd love to have some pictures but it disappeared (this family loves bread) with dinner last night and french toast this morning.