I think your question is the time interval from surface quenching to tempering, not how long the heat preservation lasts, right? If the time interval is a little longer, generally speaking, it should be tempered in the furnace immediately after quenching, and the time interval should not exceed one hour, but considering the actual production, it is no problem to take a long time. I did this in actual production. The material of this part is 45#, and its shape is relatively simple. I suggest that you adopt self-tempering to reduce the cooling time and the residual temperature of the quenching part.