It's toxic to everyone. Same applies to rats. Watch for the same signs, drooling, pawing at mouth ect. It can cause permanent kidney damage. You can use pepto bismal at home to help ease symptoms. If he can't breath he needs to go to the vets.

Hopefully he is ok.

 

Any idea how long until symptoms would show?

 

I think it should happen pretty fast. Though I did see one mention of it happening days afterwards, but I wouldn't take that article as a reliable source. Probably worth watching him a few days, but I think if you haven't seen anything yet, he's probably ok.