My mother used to ask why a time capsule would be opened after only 50 years. "There are people around who still remember that long," she said.
It's a good question, even though part of the answer is fairly obvious. Often the span of time that a capsule is to remain buried is set by younger people who have a hard time imagining 50 years into the future. As the time capsule is buried, five decades seems like a long time to them. Then, too, people may have a desire to be a part of the remembering. If the question were raised, "Shall we open the time capsule now, or leave it in the ground for another 50 years?", people might well answer, "Let's open it now. I won't be around after another 50 years and I don't want to be left out." And when the contents of the capsule are laid out for everyone to see, the old folks will be heard to say, "I remember that ... I haven't thought about that for 50 years!"
To the extent that a time capsule's purpose is to tie personal history into an integrated whole, half a century is long enough. And if the purpose is to open an opportunity to link experiences between one generation and a successor, then 50 years is long enough. But if the goal is to archive some tokens of how life is experienced today for the edification of future generations who have no link to our time, then 50 years is something of a joke.
The question, as is so often the case, comes down to the primary purpose for burying the time capsule in the first place. Who are the intended beneficiaries? What benefit will they receive? How will sealing a few objects into a capsule and then burying it in the ground or sealing it into a wall help bring that benefit? Is there some better way to accomplish the same purpose?
If the goal is merely to integrate the lifetime memories of a few people, a get-together at the local senior center with old photographs and other memorabilia would likely serve the purpose far better. If the goal is to link the memories of one generation to those of the next, a decennial retrospective by the local museum, library, or achive center would be a possible alternative.
If the goal is to preserve tangible evidence of present-day life for people who no longer have direct contact with that history, fully funding broad-ranging historical preservation centers would likely be the best approach.
Of course, making that last play in actual reality requires a longer view and a larger commitment than just burying a tin can.