From the horse's mouth.
From the Wyeast FAQ website:
3. Does the package need to be fully swollen before pitching?
No, The package can be pitched before activating, or at anytime during the activation process. The activation process "jump starts" the culture's metabolism, minimizing the lag phase.
Smacking though fun, is never really necessary.
Making the starter is all that matters, not whether or not the pack inflating. It's fine!!!
There's no need to start with a smaller starter or anything. Just proceed as normal.
Heck I rarely even bother waiting for it to inflate, I pop the nutrient pack, give it a shake, and dump it into my starter wort. Saves waiting.
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Revvy's one of the cool reverends. He has a Harley and a t-shirt that says on the back "If you can read this, the bitch was Raptured. - Madman
I gotta tell ya, just between us girls, that Revvy is HOT. Very tall, gorgeous grey hair and a terrific smile. He's very good looking in person, with a charismatic personality... he drives like a ****ing maniac! - YooperBrew