Was it just fertiliser or a weed and feed type of product?
Does the packaging say anything about it?
If it was weed and feed then I wouldnt put them on that area for the rest of this year.
If it was just fertiliser, then I believe most of the fertiliser is used up after about eight weeks, particularly if there’s been lots of rain. But you would need to check the product packaging, perhaps call a vet but personally I’d err on the side of caution