I've found that my smack packs take at least 3 hours to fully inflate in a 75 degree room. I've pitched packs that haven't fully inflated with success, but I've found that fermentation is quicker if I allow the full 3 hours.
Depending on your yeast, 68 might be getting too hot. Which yeast is it?
Primary: North of the Border Vienna
Secondary: West Coast Blaster
Kegs: Common Room ESB, Belgian Wit
Bottles: Steinbart's Oatmeal Stout