I don't think it's too late.
If chocolate poisoning is discovered and treatment begun within three hours before any overt signs have developed the veterinary surgeon will often empty the stomach by giving a drug to produce vomiting. This may be followed by an adsorbent charcoal mixture into the stomach. This will help stop further absorption of the theobromine and reduce the signs that subsequently develop.
http://www.parkvets.com/petsandvets-chocolate.html