You are working with flammable and noxious vapors. Read the
precautions on the can of the Polyurethane before you start. Consider finding a room with no open flames, good ventilation and a low dust environment.
For an Unblown Egg-Your could varnish eggs that are unblown, but you would only apply one coat of varnish; this would allow the egg to breathe, avoiding an explosion while the liquid egg is drying out, over time.
For a Blown Egg-I like to apply up to 6 coats of varnish for each pysanka. First, I drain the egg after the wax is removed and the pysanka design and dyeing is completed. I let each coat of varnish dry inbetween, allowing for a minimum of 24 hours per coat. I think of this time as “curing” the varnish on the pysanka. Most of the time, I wait until I complete about five pysanky and then varnish them all at once, as you see here.