I have and it seems not to have been a problem. But I agree it would be better to run it a few hours beforehand and shut it off while actually working - you room’s airflow patterns will vary, to corrupt a phrase.
I hope you’ll update use when you’re done, to know if the advice helped, and maybe a picture.
The Bar Top finish that has been mentioned is a Two part epoxy product like this
In boat varnishing some people use a two part epoxy or polyurethane to get the build and depth with a product mentioned above or something like this A bit of caution, if the piece will be outside use an exterior grade product. Epoxies are not UV stable and will still require a coat or two of Exterior varnish to keep the Epoxy from breaking down in UV.
A couple of other tips that have not been addressed
Do not dip your brush out of the can/container, pour enough varnish for the coat you are applying through a fine paint filter into a clean cup and work out of it.
Selecting the right brush is only half of the battle. Proper brush maintenance is the other half. One school of thought is to not let the brush dry, to keep it in solvent or cleaner suspended so it is not touching the bottom or sides of the container, the thinking and from my experience is that it is difficult to get all the solids from the varish out of the brush, if given the chance to dry, they will come out of the brush with the next use leaving particles in the surface you are finishing.
Someone gave me this tip when I built my wife a bookcase: instead of using fine steel wool or sandpaper, I used brown paper (from a brown paper bag) on my sanding block, after each coat of varnish. It came out great.
The problem I’ve found with using steel wool between coats is that it doesn’t really level up the coat you’re working on. If you have any dust embedded in the varnish, the steel wool will round it over a bit, but not bring the whole surface level, though you tend not to see that until you apply the next coat. That’s why a sanding block (felt is nice) with fine sandpaper is good – though it’s a little unforgiving. If the wood surface underneath isn’t flat, you can sand back to bare wood on the high spots really easily. And edges are always a problem.
Suffice it to say that getting a great finish isn’t easy.
It helps to put the varnish on in very thin layers.
You first layer on the raw wood is what will seal it, and this needs to be especially thin, it depends upon the specific varnish type, but you might also find it is better to have the first layer thinned out. Let this layer dry out good and hard and then when you rub it down it will take away any wood roughness.
Stand your varnish pot in warm water and let it warm up.
Varnish becomes considerably thinner, allowing it to spread more easily and so there is much less chance of runs.
The varnish will cool quickly when it is applied, but it does stop you overloading the brush.
You are best to put on one layer and let it dry for 24 hours if you can, you may well need 10 coats of varnish done this way as each coat is so thin.
Don’t get too ambitious with the fine abrasive, it should not be much more than a wipe down.