If you are using it for your wedding, I would recommend putting them on the day before. I have experienced one or two coming off after three days. Make sure your nails are clean before applying to help it stay on longer.
Put them on the night before. This will allow you to get used to them but make sure they will still stay on for your wedding. Also, keep nail glue somewhere handy in case somehow a nail pops off it'll be easy and quick to reglue.
I'd make sure to prep the nail underneath, meaning no polish, no oils or lotions, perhaps a quick buff to create a good nail surface and if you don't want missing nails by the end of the night, opt to apply some crazy glue.