im fairly sure that any mice who have eaten rentokill poison would be dead within a fortnight as mice arent that hardy, and the way the poison works is that they bleed internally , and thier instinct would be to hide i would wait a week and go round your house and garden and do a thorough sweep for bodies and if you dont find any i would say that you not going to, but make sure if you do get a cat that you let your neighbours know and ask them not to put poison down as them doing this could poison the cat
We have a mouse problem, have tried everything from humane traps to rentokil and nothing has worked. As it happens we want to get a cat anyway, but are also hoping it will help scare away the hardy urban mice that have been hounding us for years. However, rentokil only recently came to remove their useless traps and poison so there's an outside chance I suppose that one of little blighters has eaten some of the poison but not enough to kill it. If that were the case, and the new cat caught it, would it make them really ill? Or are they more likely to just play with, rather than eat, the mouse?
I'm told the life cycle of an urban mouse is up to a year but I'd really not wait a whole other year before getting a cat.