The greatest show on earth, in one of the greatest cities on earth

It is entirely fitting that it should start with a stopped clock. At 9pm tonight, when that grand timer in Trafalgar Square – which almost failed to start – finally reaches zero, it is indeed the beginning, but it is also the end.

The end of "out-of-control budgets", the end of the "ticketing fiasco", the end of the "security debacle", the end of "question marks still hanging".

The end of all the politicising, and the beginning of what you could be forgiven for forgetting it is all about. Finally, the suits are off. At last, the lycra. Let the Games begin.

The running, the jumping, the synchronised swimming, the unsynchronised swimming, the rowing, the shooting, the taekwonding, the pommel-horsing and every other feat of spectacular endeavour, starts now.

For a short time, we still have the raw excitement of not knowing what new chapters London will contribute to the Olympics story, the one in which Usain Bolt almost walks over the finish line to smash the world record. Or where Kelly Holmes's eyes widen as she realises she's finally taken the last chance she will ever have. Or where a diminutive child gymnast lands with a perfect bounce on a mat, confounding the scoreboard operators, who don't know how to display a perfect 10. What will be our billion-dollar photograph? It is a tantalising prospect.

And one, after all, that will be over fairly soon. It is not a long time, two weeks, when you think of what passes in seven years. Where were you, seven years ago, when Jacques Rogge opened his envelope on a stage in Singapore, and read out the word "London"? When Lehman Brothers was about to report its biggest-ever profit, and not many of us had heard of a politician from Hawaii with a foreign-sounding name?

It is in these two weeks, not the previous seven years, that where once stood piles of discarded fridges on top of millions of tonnes of toxic earth, hundreds of the planet's most talented, most dedicated and for the most part rather young people, will be going about the business of determining what does or doesn't get written on their gravestones in front of a watching world, .

Things will, inevitably, go wrong. Trains will be cancelled, platforms rammed, taxi meters will tick towards eternity while the traffic never moves and the big boys zoom past in their BMWs on their way to some other segment of the Greatest Show on Earth to which you probably haven't got a ticket. But just for a short while, try to be nice. After all, we've got guests.

Jamaica House with its jerk chicken stalls, and giant Bolt-watching screens, is installed in the O2 Arena. Russia Park, with its outdoor skating rinks in the middle of August, is open for business in Kensington Gardens. The Swiss have taken over the Glaziers Hall in south London and are inviting the world to the Bernese Games next weekend, with promises of "folk wrestling" and "cheese rolling" contests.

The giants of the American basketball team are stalking the streets of the West End. Slovenian swimmers are furiously tweeting pictures of themselves on Tower Bridge. Wimbledon's Centre Court has been turned temporarily fuschia.

Despite the cavalcade of corporate sponsors that have both blazed its trail and followed in its wake, the Olympic Torch has been greeted with a tidal wave of goodwill on every step of its 70-day, 8,000-mile journey.

So, if you really don't think the Olympics coming to your capital city when it is, for the time being at least, one of the greatest cities on earth, is not something worth telling the grandkids about, do bear in mind that there might come a point at which they'll ask you about it.

You have two weeks to decide what you want to say back to them. If it's: "You would not have believed the traffic!" or "Oh the queues to get on the Underground, the queues! The queues!" then brace yourself now for their dawning realisation that granny or granddad might not be all they're cracked up to be.