Yes, it'll work. It says nothing about them having to sell in that time, only that they have to be listed and made available for sale during that time. In other words, if you list them but schedule them to start at a later date (than the promo period) you'll be charged according to when they start. If you list them today but schedule them to start during the promotion period you won't be charged a listing fee.

The bit about one category is referring to individual listings.  It doesn't mean that everything you list has to be in the same category.