If a cat is lactose intolerant, symptoms may appear in about two hours after drinking milk. If the cat is not lactose intolerant, symptoms may not appear after drinking milk. Feed a small amount. It's okay.
Tips:
Cats who are lactose intolerant will suffer from vomiting and diarrhea when drinking milk. You can feed them some probiotics, and then Observe it. If it does not improve, it is best to send it to a pet hospital for examination and treatment.