Now motor vehicles in Shanghai are found to be in violation of regulations by electronic police. How many days will the traffic police inform the owner?

Traffic police don't deal with violations, they deal with illegal acts.

Electronic monitoring and capture equipment, after the illegal act is caught, the traffic police can inform or not, and there is no specific legal provision. Under normal circumstances, if the same illegal act occurs three times in a row, the traffic police will notify you by SMS according to your registered phone number or by email according to your registered address.