Xclusive, I think there are no limitations in regards to when cops can legally issue a ticket.
To give you an example, I have a friend who was driving on the opposite side of the road when cops went passed. They pulled him over and fined him because in the cops professional judgement he "appeared" to be going 15km/h over the speed limit.
Now, I wasn't in the car but knowing my friend he probably was driving like an idiot and deserved it, but nonetheless this seems to be a ridiculous abuse of power. Lucky for my friend the cop made a mistake on the posted speed limit and had to cancel the ticket, so I don't know how this would have stood in court had my friend protested it.