The timing distinguishes a cold-start problem from a change during sustained operation. It can guide professional assessment, but it does not prove a thermostat diagnosis.
What the observation means
Record the selected mode, approximate elapsed time and whether the display, fan or whole appliance changed. Cooling and restarting later may temporarily hide the symptom without resolving it.
A useful next step
Use observations already made rather than running repeated warm-up tests. Stop use if heating is uncontrolled, power trips or abnormal smells occur. Explain whether the oven returned after cooling, but do not treat that recovery as evidence that continued use is safe.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.