Vallejo's varnishes are tough, and I mean tough.  I absolutely love them, especially the matt which provides a near dead finish without lightening the color hardly.  They take even longer than the paint to fully cure but can be worked as soon as 24 hours after applying.

Now I did have a bit of a hard road figuring out how to best get them to airbrush.  When I first tried them I did so strait from the bottle but found they gummed up at the needle/tip a lot, so much so I was in the habit of having a qtip soaked in cleaner, wiping the head down ever few minutes.  I tried lowering the pressure and thinning, which is the conventional wisdom when faced with tip-dry.  First with just distilled water, then with their thinner.   It was better, but not by much.  Then out of frustration one day I tried upping my pressure... and just like that they worked perfectly, even strait out of the bottle.  I would get through an entire coat without needing to wipe the tip even once.  We can debate the science of it but bottom line is they (apparently) just need to "move".

Gloss is a tad trickier in that you need to really shotgun it if you want a truly gloss finish. If you go lightly you will get a "texture".  I recommend thinning with some water, between 1:3 and 1:4, and really hit it.  If it looks like its almost going to run, you are there.  It WILL shrink while it cures and tighten up nicely.