90 Days
I had an accident in April, thought nothing of it, becuase it was so minor, and never told my insurance.
3 months later i was been sued for damages!!!
To cut a long story short, i had 90 Days to tell them of an accident or my policy was going to be void.
Because the date from receiving the claim, for personal injury, and having the accident was after 90 days i had to write a letter telling them why i din't disclose it.
If you have an accident tell them straight away, it could affect your cover if you don't. I learnt the hard way.
The short answer is around 90 Days.