你的车什么时候停进来的，白衣人并不能知道精确的时间。只要白衣人来查的时候，你的coupon已经开始生效即可。

Idling engines Under the Environmental Protection and Management (vehicular-emissions) Regulations, it is an offence for the driver of a motor vehicle to leave the engine of a vehicle idling while it is stationary, for reasons other than traffic conditions. The rationale is to prevent unnecessary pollution and at the same time reduce fuel wastage. Exceptions include vehicles where the engine is needed to be running for operation of on-board equipment, moving vehicles in a queue, vehicles undergoing inspection or repair and enforcement/emergency vehicles. Owners who leave their vehicle engines idling can be fined up to $2,000 for the first offence and $5,000 for subsequent offences, if convicted in court.