Example: Froslass has a 01.75 second cry and I know that isn't it. The reason why I said Black and White is because the cries may have changed, but I dunno.
Pidgey's cry, at 0.181 seconds, is the shortest in Generation V.
Cry (Bulbapedia)
Snorlax or jigglypuff source (I don't know how to male it short) http://www.gamefaqs.com/boards/946308-pokemon-platinum-version/50256717 jiggly puff at http://bulbapedia.bulbagarden.net/wiki/Talk:Snorlax_%28Pok%C3%A9mon%29#Shortest_Cry.3F
>I've heard a lot of cries, but I'm pretty sure Snorlax has the shortest. Yeah Snorlax and Jigglypuff both have a pretty short cry. I think Snorlax just has a tad bit shorter of one.
So, Snorlax. No idea how long though.
Source