Mine are Walker Zanger same as nightowls and we also sealed-DIY. I used miracle 511 and a foam brush. I laid an old sheet out on the table and laid out a 'batch' of tiles. I brushed the sealer on and wiped it off with a cloth according to their directions. *It did say if you let it dry too much before wiping it could streak when you wipe so you'd need to re seal and wipe again. I had that a couple of times but really even though I panicked it was no big deal at all. Did it all pre install. We also used Mapei flex color cq white grout which does not need sealing so I left it at that. It's been 6 months and no issues with staining or further cracking either.
You can do it!
edit: oh and I second EAM-follow the mfg's instructions/recommendations.
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Tile sealing
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