Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your 25 to 30 pound pups got into a bottle of Tylenol and ate roughly four tablets. I assume these are the regular strength 325mg size?
We see toxicity symptoms in dogs at a dose of acetaminophen higher then 75 mg per kilogram (2.2 pounds per kilogram) of body weight.
At 25 pounds the smallest dog is 11.36 kilograms (2.2 pounds per kilogram), so he would need to eat 852mgs of acetaminophen. (11.36kg X 75mg/kg = 852mg) to see toxic signs.
The usual tablet size in milligrams is 325mgs, so if the 25 pound dog ate four of the 325mg size then he ate 1300mg, which is a toxic amount. If he ate three of them then he ate 975mgs, still a toxic amount, and if he ate two (650mgs) or less then that would not be a toxic amount.
At 30 pounds your other pup is 13.63kgs, so he would need to eat 1022mgs of acetaminophen (13.63 X 75mg/kg = 1022mgs).
If the 30 pound dog ate four of the 325mg size then he ate 1300mg, which is a toxic amount. If he ate three of them then he ate 975mgs, which is not a toxic amount.
After 5 hours it is probably too late to induce vomiting, but it would be worth getting your pups to an emergency clinic to have blood levels of acetaminophen checked, and give several doses of activated charcoal at 1 GRAM per pound of body weight, as if any ate all of the tablets they would get sick. They can also give drugs to counteract the toxin.
Signs to watch for with acetaminophen toxicity would be brown or gray colored gums, difficulty breathing, edema or swelling of the face, neck, legs or feet, vomiting, yellow color to the skin and in very severe cases coma. These symptoms can take hours to 1-2 days to start, so ideally we would start treatment now, even if they seem fine.
Although I recommend treating them tonight if you choose not to treat them at the emergency clinic I would encourage you to get them to drink plenty of water tonight and watch them closely, then have them see their regular veterinarian tomorrow.
Please let me know if you have any further questions.