I live in a desert and I've been using the instructions here and I put Lexol on when the bag is still damp, maybe several coats,then later Blackrocks. Sometimes more than one coat of Blackrocks. It's kind of like petroleum jelly.
To slow down the drying I also lay a towel across it, making its own microclimate under the towel. This might be helping only in my mind, though.
That sounds like a good technique but I have had a few bad encounters with mildew in the past. Maybe mildew is not a problem in the desert but it can be a pain in the neck in the Midwest! But I also sometimes wrap up a bag in towels that seems to be drying too fast, especially the strap or other thinner areas.