The instructions said to let the glue dry, so I let the tiles wait... a week. Not that they needed an entire week to dry, but life intervened...
Meanwhile, I examined the two tiles to see how the flocking turned out. The first tile definitely had more "turf," but also had "dead areas" where brown static grass had glued lying down. The second tile had a more uniform coverage, and the static grass didn't seem to be lying down... but the flocking was less dense.
Both tiles had patchy areas along the edges. This surprised me, as I had gone to special efforts to make sure I had covered right-up-to-the-edges with flock.
So when I had time again, I laid out my tarp and my tiles, and prepared to finish up by cementing the grass into place.
The product they sold me on to permanently fix the flocking in place was something called Matte Medium - Transparent Scenery Cement:
Matte Medium is our most economical transparent scenery cement. Matte Medium will never dry out or deteriorate. It will never turn yellow like regular household glue and will always remain flexible. Matte Medium is ideal for foam textures, ballast and most scenic applications.
It is supposedly superior to white glue because it is a synthetic acrylic-based adhesive that dries matte and clear, with greater holding properties.
I bought the concentrate, so I had to mix up a batch...
Bypassing the recommended non-clogging Spraymister, I instead bought a sprayer at my local $1.00 USD store. I marked the proportions on the bottle with a Sharpie - one part Matte Medium, four parts water, plus a dash of dishwashing detergent. (OK, I marked the bottle wrong, but I noticed my mistake before mixing up the batch!)
Then I started to squirt down the flock. Though at first, I was shooting big streams of glue...
...but eventually I got it down to a fine mist...
After the glue dries, I go in with some Tacky Glue (a thick white craft glue) and try to fix the "bald" spots (particularly around the edges). On the Grassmaster'ed tile, this begins to look like a frilly edging, so I sprinkle more flocking over that tile. Then I again mist both tiles with the Matte Medium, and let them dry overnight.