Pizza — Food safety facts
Feed with care · Cats · full breakdown on the linked food page
The dough, cheese and sauce bring salt, fat and usually onion and garlic powder.
Short answer
Signs like vomiting or diarrhea could appear within a few hours, but it depends on how much they ate and their sensitivity. Mild tummy upset might pass in a day, but watch for lethargy, loss of appetite, or any signs of pain. If you see these, or if your cat ate a lot, contact your veterinarian for advice.