Does anyone float their eggs to see if they are fertile?

I know it kinda works, because I have done it with my canary eggs.
I have a heap of button quail eggs in my incubator that I just can't candle and I was wondering does it work with those eggs too.
Some of the older eggs have passed their due day by 4 days now. I floated all of them and more than half sunk
Has anyone ever floated button eggs and how long should I wait to see if any of them hatch?
My canary eggs would often go over due because I have a home made still air incubator with no thermostat.

 

Hi Hinkjc,
Your friend is so correct about the candling. I even kept the eggs in there that I thought weren't going to do anything and when I floated them a couple started dancing in the bowl of water.
Button eggs must be the hardest dam things ever to work with.
I have hatched many different species in the past and could tell almost within 5 days if the egg was going to make it to hatch.
And now I have a heap more eggs waiting to use the incubator, so trying to figure out what goes and what stays.
Thanks for you reply and have a nice new years.

P.S. got one of the almost toss outs pipping now. Those crazy button eggs!