On Meindl Perfekt Hunters: I Sno Seal with as much as I can work in when they are clean and new. Let them sit in the sun for a day when it is hot (some use a hair dryer to speed up the soaking in/saturating process). I then give them a second coat of Sno Seal and sit them in the sun another day. After that, I re-apply Sno Seal when the boots are getting dry.....usually around the toe area where the rocks and grass abrade them and they start to take on moisture, frequency depends on use. On longer backpack trips I carry a small zip lock bag of Sno Seal and re-apply to the critical areas as required, usually once on a 14 day hunt above treeline. FYI, Sno Seal makes outstanding bowstring wax too and is all I use for that application.
Zamberlan has their own hydrobloc (I think that's what it's called) that they recommend on most of their boots. You might want to check with them to see what they recommend on your particular boot. The hydroboc appears to be the same thing as Nikwax.