I'm quite certain that nothing get's expired or goes bad in this game. Before I thought if we didn't collect the egg after breeding, 1 of the dragons would run back to it's habitat and leave the other behind (because I saw 1 dragon in the Breeding Dens at a few nbrs' places). It turned out to only be a visual bug. The game has been out for a while and no one has experiencing things gone bad or expired and I've left things untouched an entire day without problem soo ..