The problem could be either the oven or the wiring. The oven could be using more amperage than the circuit breaker is rated for, and thus tripping the breaker. Or, the problem could be with the wiring (for example, damaged insulation causing unwanted current in the wire), or the circuit breaker could be failing.
Standard circuit breakers are designed with a certain amerage-time trip-curve. For example, a 30 A breaker should never trip while it flows 30 A, and at twice the rated current (60 A), could trip after as long as a minute. It may trip within a second only for ten times the rated current.... This is the expected behavior, and does not indicate a malfunction. For an example curve, see this Siemens document. Your oven could be using more than the rated current when on, but since it is only continuously on during warmup, it would only trip the breaker during the preheat stage.
Newer installations could have special types of breakers, such as GFCI or AFCI. But, this would be unlikely for a dedicated appliance circuit. Loose connection could cause series-arcing, but this shouldn't trip a standard circuit breaker (it would reduce the average power being used). If the appliance was connected to an AFCI breaker, the breaker could be detecting the arc and tripping.
In any case, correct the problem soon. The circuit breaker is likely not designed to be used as a switch, it has a limited number of trips during its lifetime. Also, the fact that it is tripping signals that something is wrong (and probably overheating), and likely unsafe (possibly causing a fire).
Electricity is dangerous, and you should only attempt repair if you are comfortable around electricity and know the proper safety precautions. working in the circuit breaker panel is especially dangerous, and you should wear a face shield and other protective equipment, in case there is an arc, or a circuit breaker explodes.
My gut feeling is that the breaker is likely failing, and should be replaced. I think this because ovens will usually "fail open" causing their current to go to zero, not increase their power used. Also, running the oven all day would put additional stress on the breaker. The oven is likely powered with 240 V split phase electricity (common in the United States). In this case, it would have two "hot" wires, one "neutral", and one ground.
I would go about troubleshooting with the following steps:
Verify the breaker is of the correct rating. Examine the information plate on the back of the oven for the maximum current that it requires. Ensure that the circuit breaker is rated for that same amount of current, or the next higher standard amperage. The standard breaker sizes include 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110 A, et al. Read the NEC codebook for details on which breakers you are allowed to use. If your circuit breaker is undersized, then verify that the wiring and plug is sufficiently large to support the needed current, and make the necessary corrections to the setup.
Measure the actual current going to the oven. In the circuit breaker panel, attach a clamp-type ampmeter to one of the hot wires going to the oven, and measure its current while the oven is turned off and also during the preheat. The current while it is off should be near zero, and the current when it is on should be less than the oven's maximum current. Repeat this with the other hot wire.
- If the preheat current is less than the rating of the circuit breaker, the circuit breaker is faulty.
- If the current while the oven is off is significant (>0.3 A), then either the wire to the oven is bad, or the oven is damaged. Unplug the oven, and check if the current goes to zero. If it doesn't then you have wiring issues in your home.
- If the off-current is near zero, and the preheat current is more than your oven is supposed to use, then your oven needs repairs.