A sensor-based or automatic mode may revise its estimate as it runs. The manual should explain whether the displayed time is fixed or adaptive.
What the observation means
Changing food quantity, opening the door or using a different container can affect the conditions the programme monitors. A revised estimate is therefore not automatically a timer fault. However, an unexplained stop or error message needs its own description.
A useful next step
Record the programme name and what changed around the time adjustment. Use the food's completion checks rather than treating a countdown as proof of safety. If the programme loops indefinitely or produces repeated poor results under its stated conditions, report that pattern without running extra test meals.
Manuals and supporting guidance
Model-specific instructions take priority. These references support the practical principles discussed here; they do not diagnose your appliance.