End of the month.

Personally, I keep my old flares too if they're only slightly out of date. Mr. Murphy will bite you when you least expect it and something is bound to happen where you either A - Use up all your new flares, B - Your new flares got wet and you didn't know it and don't work or C - In the excitement of declaring your emergency you drop the flares overboard. So.....I like to have a backup. I keep the new ones handy for inspection if the Coasties want to take a look and keep the old ones on board as backups.