So...one of my villagers asked me to bury his timecapsule. I did, and mentioned to him that I buried it. He just said "awesome, I will tell you when to dig it up again"....and....now it's just...buried there. How long is it supposed to be buried there? I always think it's a fossil and try to get it xD haha
just leave it. it'll disappear eventually and then they'll ask you to dig it up.
just remember where it is. i usually just plant it near their house.