I try to use all coated sheets on the day I prepare them. I have in the past used sheets that have been in a box for over a week and not noticed any problems, but I've also read things that imply it's best to use fresh paper (though I can't remember the source, what supposed to go wrong, and haven't tested this). Not a full answer, but I hope it helps a bit Marco.
The biggest problem with storing pre-coated papers is desiccation or drying out of the paper. If you want to store paper long-term (more than a couple days), you need to completely de-hydrate it and store it in arid conditions (ideally in an airtight container). Otherwise, the partial humidity in the paper will cause changes in the sensitivity and responsiveness of the emulsion. If you do completely desiccate a pre-coated paper and store it in an airtight container, you will need to thoroughly re-humidify before printing. Frankly, this is a pain in the butt and not easy to do properly. Best to just coat as you go.