When questions my insurance company said there was not a time limit but if I made a claim regarding the rig and it was found to be in poor condition I would not be covered. Pretty hard to check the condition if it was all at the bottom of the Solent somewhere 😉
I use Continental All Season Contacts, seem to do fine, wear wise, and handle in both warm and cold, I drive a Volvo V60, mainly motorway at moderate speeds.