Bubbles should start to form on the surface of the egg almost immediately.
Vinegar is needed.
there will be no eggshell left but the egg membrane will hold it together.
you will be able to see the yolk through the membrane
some vinegar will seep into the egg causing it to swell up
It does not turn into rubber.
The egg shell contains calcium carbonate which is a salt.
vinegar is not the only liquid that can dissolve an eggshell