Oh, a day is a different story, I was thinking no more than an hour. That is why my firemaking gear is in metal or plastic hard containers, and that are then waterproofed with tape or a bag. Or with a little bit of grease if a matchcase. If I'm in a canoe or a boat, they go into match cases, which go into a zipper bag, which goes into a second one, which gets wrapped in duct tape. Dry is good.

And after a month underwater, I don't expect anything but sea life and submarines to work right.

AFAIK, lighter and sparklite flints are ferrocerium, which has known issues with oxidation. As small as they are, adding water is accelerating the process. That's why you inspect your gear regularly, and carry backups in a weatherproof container if it is critical. My first sparklite is... I don't remember how old, and that is the one I keep in my PSK as I lost the case for it. That gets tested every few months, and if it gets immersed, as soon as possible. I dry the entire kit out under a light bulb and replace the matches and lighter at that point if it gets water in the case, and I sit down and think about what went wrong with my seal.

Now, real flint shouldn't have issues with being soaked for a few weeks, but the carbon steel scraper would have issues. You'd have to knock the rust off, and retouch the edge so it had a nice sharp angle again. Same problem, just with a different component. Unless you are using a fist sized lump of flint or jasper and fist sized lump of pyrite, and just banging the rocks together. :P