The clue as to why they'll be useless lies in the phrase 'in Japan'. The UK is not Japan. I think they're a great idea - if they'll be honoured. But just as liberalising drinking hours produced more drunk people, but didn't produce a Continental cafe culture, mechanisms for expressing intergenerational solidarity are likely to be more effective in Japan than here. The UK's post-war history is one long tale of ripping off the frugal, the virtuous, the far-sighted, and supporting the spendthrift, the antisocial, those who take no heed for the morrow - pretty much the exact opposite of the previous two hundred years. The chances of a few hundred 'care hours'* clocked up in the next ten years entitling one to corresponding hours in the year 2035 are minimal, unless some kind of cultural revolution occurs.
In Japan, the system, called Hureai Kippu, was established in 1991 and has been expanding ever since as a way of helping to manage the country's rapidly ageing population. Literally translated as "Caring Relationship Tickets", it allows a volunteer to "bank" the hours they spend helping an elderly or disabled person in their personal Time Account. Different values apply to different kinds of tasks. For instance, more credit is given for helping at anti-social hours or with personal body care. Household chores and shopping command less.
These healthcare credits are guaranteed to be available to the volunteers themselves later in life, or to someone else in need, within or outside their family. The local and national government has even set up a nationwide electronic clearing network, so that a person can provide help in Tokyo, while their time credits are available to their parents anywhere else in the country.
Now it could of course be that said cultural revolution has arrived, in the shape of George Osborne and his outrageous plans to reduce Housing Benefit to a maximum of only £20,000 a year, a policy which it is feared will cleanse Kensington and Queen Anne's Gate of all their minimum-wage householders. The Big Society will reward the deserving, and the undeserving will be made to attend frequent interviews with outsourcing companies - or something like that, anyway. That's the theory. Do you believe ?
To paraphrase Apocalypse Now :
"Do you not approve of the Big Society ?"
"Sir, I don't see any society"
(* don't think Laban is a basically selfish chap. I spent fifteen hours one day last week, of which nine were driving, picking up an aunt (who's had a stroke) from Banbury and taking her to Gower for the afternoon to visit her sister. Don't get me started on how much diesel that was. I just can't see a 2035 government sending anyone round to do the same for me.)