I would wait for 72 hours even after a big rain storm. Reason is - that plants absorb the poison almost imediately and that its probably still in the plants that were sprayed on. If you leave it for a few days, usually the toxicisity will go down and that it will be safe for your cats. I know that Bastet doesn't go outside without my supervision and definately not after the next door neighbours have sprayed anything.

Fertilisers to pets are just as dangerous as weed killer is. Some animals can't absorb the lime and other *enriching* soil substances. They end up affecting the liver and kidneys. So if you decide to fertilise, use a natural, water soluble one that immediately goes into the soil.

BTW <- AVID gardener *grins*