All your valve timing is dependant on the length of your chain... your IP timing can be set to compensate for wear.... How much are you willing to live with ...
One clue may be the Number of degrees that the offset key is designed to correct.... maybe they thought you could deduce from that what they considered too much...
Otherwise it is sorta what you are willing to live with... it is a tedious but not hard job to put in a new chain.... and keeps your cam in the right place at the right time....

http://www.peachparts.com/shopforum/showthread.php?threadid=29818&highlight=tcane+chain+stretch