For most insurance companies you must file the claim for the car accident within 2 to 3 years otherwise the insurance company cannot and will not do anything about the car accident.
Ideally you should file the car accident claim within a few days to a week after the car accident.
The sooner you file the car accident insurance claim the faster the insurance company can get to work on paying you out for the car accident if you are entitled to a payout.
I've never waited longer than a week to file the insurance claim for a car accident because I do it while it's fresh in my mind.
After a month or so I would likely forget to file the car accident claim and by then the other driver could be long gone somewhere.
So if possible file the car accident insurance claim within the same day or a few days after the car accident.