Hi Peggy, you can certainly bake your bread at  400°F instead of 450°F, although you may get a little less oven spring and perhaps a slightly less crusty crust. If you put the pot and bread into a preheated oven, I would remove the lid after 25 minutes and continue baking until the loaf is done. I would guess it's likely to take another 20-25 minutes, but look for the usual signs of doneness--rich brown color, firm crust, bottom sounds hollow when you thump it. Internal temperature should be at least 195°F. 

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