IT WOULD seem that among the many variations in food and its complex relationship to our social habits, in our 'culture' (in the broad sense of the term) none is greater or more determined by extrinsic factors than the time at which we eat. Our biological clock may make us hungry at all sorts of times, but convention dictates that we should only eat at certain specified hours. From country to country the dinner hour, that product of high culture and wealth, wanders all over the clock. Each society knows its hour and it is only the alien who has to inquire.

Thus it was that in Tokyo one fatal day (fatal for one hates to be ill-bred), I accepted a dinner invitation from my old and enormous friend Shinoda Hajime, a scholar so worldly-wise that he was simultaneously known at his several universities (the Japanese professorate is so badly paid that all dons have multiple jobs) for three things: his considerable capacity for, and knowledge of, the finest French wines, his admiration for little-known British composers and his passion for South American literature. No cultural slouch, then, but a man who, on his first visit to London, was able to guide me unerringly to the Holst house and tell me where Constant Lambert worked.

But also Japanese, and therefore a man for whom ceremony meant a great deal. He would, I knew, not only prepare a fine meal (or his wife and assorted caterers would), serve the finest wines in his collection, ruin the family's finances for that month, but would also assemble the choicest company. It was an occasion to which I looked forward. With only one tangential worry. Hajime had not specified the hour.

You will say that a sensible man would have telephoned. Well, not only am I a complete neurotic about the telephone in general but I do not believe it ever works, at least for me. And though I had then a little Japanese, it seemed to me far too difficult to get through to my hosts. Observation, I thought, ought to do the trick. Restaurants would presumably be crowded at the appropriate dinner hour. Wrong. They appeared to operate on a 24-hour clock.

My next surmise was that Hajime, being a highly civilised man would, in emulation of his revered British composers, French wines and Latin American writers, serve dinner in the grand European style, say at 8.30pm. But this, too, caused me some anxiety. What if I were wrong? America's influence on Japan was great. They might well eat at the hugely unsociable American hour of 6pm or 6.30pm (Americans eat then on the odd theory that family life consists of bolting down food in time to watch prime time television).

The more I thought about dinner, the safer it seemed that I should be early rather than late: a few hours of conversation would hurt no one and the only rudeness could be if my hostess was still in her bath. So nervous had I become that I summoned a taxi for five (fortunately, for it takes an hour to get anywhere) and was disgorged up a tiny alley into the Shinoda household at six sharp - to find, when I worked my way past the books piled in 6ft-high piles towards the dining room, a dozen people sitting cross-legged around the table and, though too polite to show it, slightly cross.

'Don't you know,' said Donald Keene, a man become more Japanese than the Japanese, and my revered mentor, 'that the Japanese dine at four?'

No, I did not. No more than I knew when I went to Madrid for the first time that one did not meet one's friends for dinner much before midnight. No more than I knew when very young (and therefore much hungrier) that one never came to dinner at the hour for which one was invited, fashion dictating that one be at least half an hour late so as to be able to make a grand entrance and feel even more welcome.

Dinner, like time itself, is a convention of society. People who are serious about work (they are those who have to work or starve) eat before work and after work, sometimes pausing briefly in the middle. The idle rich, who devise these conventions, rise at their pleasure and dine at their leisure. Italians and Mediterranean peoples generally take the middle of the day off for the serious business of eating and imagine that if they eat late at night they will not digest or sleep properly.

I confess that I am for these bizarre variations: now that I know about them and anticipate them. There is something very pleasant about abolishing the sort of time that is related purely to habit. I learnt the joys of the early breakfast in the sub-tropics: what is better than one's own mangoes or pineapples, strong coffee and fresh-baked Cuban pan de agua as the sun rises? There are days when one would wish to share a bottle of wine and a decent meal with a friend who has blown into town at three o'clock in the afternoon (no easy feat, but one of the reasons I love the brasserie concept, a meal at any time). But, paradoxically, I dislike unpunctuality in myself and in others.

It comes down to this: if you have settled on an hour beforehand and you are not living, solo, in a world of your own devising, it is best to bend to whatever culture you find yourself in. Its habits will teach you something.

However, beside this diversity I would make one small request; that everywhere there is an airport, there should be a place to eat at 6am the dinner you have missed because you could not face the airline food and because, whatever the clock says, it is really midnight in your stomach.