food grad finishes

According to gubmint sources I have read, yes it will cure up to a food-safe condition.

WHEN that might happens is the result of a wide array of factors you didn't specify and we can't predict. Your first clue will be when you can no longer smell the finish. I'd give it a good month (at least)beyond that point in the "belt + suspenders" tradition. You are looking for the solvents to depart ... the remaining solids are a) relatively safe and b) unlikely to be eaten in a significant quantity.

BTW, spar varnish is a phenomenally bad choice ... it is intended NOT to dry for a long time. But eventually, even spar varnish will dry.

Suggest you consider an ordinary wiping varnish instead and just call it a day.

Bill

Spar varnish is long on the oil component for the flexibility it will require to survive fluctuations in temperature outdoors. It also normally includes an ultraviolet inhibitor for the same reason - it's outdoor varnish.

Since it is a long oil varnish, it will take longer to cure than standard varnish, but not as long as if it were strictly a curing oil. Save that the greater amount of oil versus resin makes a softer film, it is perfectly suited to the task of keeping moisture out of the wood. Your best choice? Maybe.