Hi XXXXXXXX,
Generally snail bait takes effect with symptoms within a few hours so it is possible that he did not eat any, which would be great.
You can read about symptoms here. It a pop up shows up over the article just hit "close windows" at the bottom to get to the article.
http://www.petplace.com/dogs/slugs-and-snails-the-dangers-of-slug-poison/page1.aspx
This article talks about the main ingredint , metaldehyde.
http://www.vetmanual.org/mvm/index.jsp?cfile=htm/bc/212000.htm
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team