Any electronic device that could reveal an 'audible' difference in a matter of hours, or even days of use, would have a very short life. This would have to change the actual values of the components used, and this is not something you want to happen and it would be very difficult to limit this with a warrantable piece of equipment.
You would hope that the factory that manufactures these things would have given them a sufficient run-in to see if it would survive it's warranty period at the very least with revealing any possible weaknesses. So in that respect, yes, if it survives the first few days, weeks or months, you can feel lucky that you didn't end up with a lemon.