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This isn't going to be a timer failure, but you could have a faulty lower oven relay board, or possibly just the high limit thermostat has tripped and needs to be reset. To check, turn the circuit breaker off to the oven and open the bottom door. There is a vent panel that runs across the door latch assembly just above the oven cavity. Remove all the screws going into this panel and pull the panel off. Now if you look just behind the door latch assembly you'll see a 1" round silver and black device with a tiny red button. This is your high limit thermostat and if you press the red button it might click. If it clicks, then the issue is solved. if it doesn't click, then you'll need to replace the lower oven relay control board just under the top panel of the entire double oven.