There time and date stamped I just let mine be fo a month or so...
I do the same check them when I check the feederWe are doing ours every 2 weeks right now. Only because we fill the feeders every 2 weeks. We dont mess around and hang out. Add corn. Change SD cards and get out.
In the past when we didnt run the feeders all the time we would let the cameras sit about a month or so.