I remember years back, Nick saying that he would put a coat of varnish on a deck and let it dry on top of the car on the way to a paddle. (back in his carefree years).

True Fact. I've also put three coats on in a day with the boat out in the hot sun - far from best practice. I've also used my boats between coats of varnish: varnish Friday, paddle Saturday and Sunday, and then varnish again Monday.

Varnish gets harder over time as solvents evaporate and chemical bonds cure. So fresh varnish tends to be a bit soft and easily scratched. But, varnish will get scratched no matter how long you let it cure, you can always add another coat to make look fresh again. Just wash the boat down, sand and add another coat.