Not sure to be honest. but may i suggest you start by look at high profile prosecutions resulting from a fire i.e. New Look, Oxford Street. whether a claim was made or paid must be public information as it is a plc.
i do not think the timescale would be relevant to an insurance company. if they could prove a deficiency was identified, was risk critical, and that the deficiency directly contributed to the cause of the fire or it development, but no action was taken. Then i think they would have reasonable grounds to refuse to pay up whether it was a week or a year (i bet its in the contract somewhere)
A point for discussion;
could you say that if a premises was subject to a sucesfull prosecution. then that would be reasonable grounds for the insurance company not to pay?
I can say that i have direct experience of insurance companies being more than thorough in investigating this very issue in the past. sorry i can't expand on this but i am duty bound not to at present.