Restock is being used as a noun here, which is why the speaker says so that we waste less time on restock. Technically, restocking can also be used as a gerund (a verb functioning as a noun) to create so that we waste less time on restocking. There is no significant difference between the two phrases, and restocking can be used without changing the sentence meaning.
Ex: I like to bike in my free time.
Ex: Biking is one of my favorite pastimes.