Your question is Current-Carrying Busbar Thermal Steady State. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
How long would it take for a current-carrying busbar to reach steady-state temperature?
Give the answer as an engineering estimate, not a single fixed number. State which physical factors control the time to steady state, and what extra information you would need to calculate it credibly.
Keep the answer focused on thermal behavior of the busbar itself, not on electrical protection or fault analysis.