Do you mean the longest or shortest period you can wait?
I'd be inclined to tell your insurer straightaway that you will (or may) be making a claim. You don't have to give all the details - just tell them of your intention.
With reference to the above answer. If you tell your insurance company that you might make a claim and you don't actually claim, you are still a higher risk driver and may be charged a higher premium. I know because it happened to me. I had 2 non-fault accidents and I'm a high risk driver!
As soon as your application has been accepted and your premium paid you are fully insured and are entitled to claim immediately. Unless your small print tells you differently.