Bread failures

When 550ºF is not 550ºF.
When I'm preparing to bake bread, I normally fire my for approximately an hour an a half and put in the breads when the temperature is about 550ºF. and falling. Yesterday I put a loaf into the oven when the temperature was also 550ºF, but the oven was not falling because it had been fired six hours earlier and was fully saturated with heat. I attempted to rush the process, and I achieved a failure. The loaf was more than a little rustic in appearance; it was burnt.
A simple temperature reading is certainly not enough. I should have waited until the oven was clearly falling.