7 years
The police can hold you for as long as they deem necessary if you have broken the law and driven a vehicle with a stolen template. Every state is different.
Police in the UK can hold your license as long as is necessary to complete their investigations.
48 hours :)
It depends entirely on what reason they are 'holding' it.
Normally police can hold you for up to 48 hours before having to present you to the court to be formally charged.
As long as the vehicle itself meets the legal requirements (has insurance, current registration and inspection, etc.), and your licence is still valid (not suspended, expired, revoked, etc), and you have permission to use the vehicle, then yes. You should be more worried about the police thinking you have someone else's licence, given the terrible photography skills of the Colorado DMV.
24 hours
As long as you are driving, yes!
only as long as the vehicle is 4 cylinders. the police are aware of Canadian drivers and their high speed limits in Canadian provinces, eg. Ontario. Besides the vehicle being a 4 cylinder you will also need a permit sticker of the Canadian Maple Leaf flag that gets adhered to the rear plate of the vehicle. This prevents police officers from pulling you over for a DWI since they know that you can hold your liquor. -Miguel
20 days.
In most (if not all) states, it's illegal for a private citizen to have a vehicle that marked as an official vehicle - regardless of whether it's a police ATV or a water department car. This is why used police cars are painted over (usually badly) and have the lights/sirens removed before being sold. It's not illegal to have the same model of ATV as the police do, as long as it isn't marked to impersonate a police vehicle.
The police can hold your car for investigation for a reasonable amount of time, typically up to 48 hours without a warrant. After that, they would need to obtain a warrant to continue holding it.