You don't think so what?
Sorry I still don't understand what response time problem you think you have using the MCU as a detector.

Bypassing load for 300ms may cause damage the external circuit in case of overcurrent ?

 

Bypassing load for 300ms may cause damage the external circuit in case of overcurrent ?

So 200ms is okay but 300ms is not?
Since I don't know what the "external circuit" is, how can I know what will damage it? I'm not clairvoyant.
You still haven't explained what the load is or what you are trying to do, so we keep guessing at what you need.
If you can't clearly explain that, then I see no purpose in trying to help you further as it's still a game of 20 questions.