On the morning of a potential brewday, I took a Wyeast smack pack out of the fridge and after warming smacked it in preparation of use. Unfortunately brewday did not happen. I put the pack back in the fridge later that night. My question - Can I now still use it?
Yes you will be fine.
I recently used one that had been in the fridge for a month after I smacked it. Not a problem. The starter took right off and the beer is fermenting away happily.
Thanks for the feedback!