At 10.30 this morning, the PAs to the controllers of BBC1 and BBC2 and the directors of programmes at ITV1, Channel4 and Channel 5 are likely to interrupt their bosses to say, "They're in."
"They" are the overnights, the first data from the 4,500 meters in carefully selected households around Britain showing how many people watched what, and the five crucial tastemakers of British television will want to look at them as soon as possible.
In writing my memoir of the BBC over the past three-and-a-half decades, I thought much about what had changed and why. The big story was that the audience made the long march from passive and grateful receiver to demanding and picky consumer. Technology was their agent and enabler.
First came the video recorder, which offered viewers apparent freedom from the scheduler's plans, but in fact made much less difference than expected. It was fine for playing movies on video but not simple enough to operate for most people, and then there were all those cassettes to juggle.
The second transforming piece of technology was the remote control. To change channels, you no longer had to raise yourself from your chair, walk across the room, press the switch (or even turn the tuner), walk back and sit down again. The end was nigh for default viewing - of giving programmes a chance to draw you in. The remote was the birth-control pill of television, and it encouraged a new promiscuity.
The most sweeping change, by far, has been the growth of multi-channel households from a few hundred thousand to 12 million in 13 years. This has changed the economics and the ecology of broadcasting.
But if I had to mark the event that tipped the old world of television over into the new, it would be the day, early in the autumn of 1991, when the overnight ratings were first available to the BBC.
From then on, the first question about last night's new programme was no longer "was it any good?" but "how did it do?"
Poor initial ratings can now mean that a show is dropped almost as soon as it appears on air. ITV1 executives this month booted Hugh Laurie's new comedy series, Fortysomething, from its prime-time slot after viewing figures for the second programme showed a two million fall in the audience from the week before. The rest of the series will be shown late at night.
The ITV1 quiz Judgement Day, hosted by Brian Conley, is to suffer a similar fate after barely three million viewers tuned in to watch the second show.
Such decisions have not always been so research-based. For the first 14 years of its life, until 1936, the BBC had no research officer at all. The launch of ITV in 1955 jolted the corporation's research team into greater sophistication, but all through the Sixties and Seventies ITV measured audiences via a meter system, while the BBC continued to do so by means of daily interviews round the country. One imagined well-spoken women saying, "Excuse me. I'm from the BBC and would like to ask you some questions about what you watched on television last night." That's certainly what happened when one knocked on my door. No wonder BBC figures always suggested higher audiences for our programmes than the ITV system.
This all came to an end after the Annan Committee recommended a single system, a gold standard that all broadcasters could work from. In 1981, the Broadcasters' Audience Research Board (BARB) was established, co-owned by the BBC, ITV1, Channel 4 and the Institute of Practitioners in Advertising (and now BSkyB and Five, too). It operates a meter system, and broadcasters supplement this with their own surveys and interviews.
Many in the BBC had hoped to resist the single measurement, believing that meter-based returns would bring a reduction in the official BBC figures. (They did.) But we soon forgot the old differential and appreciated the more detailed quarter-hour by quarter-hour information.
The "grey book" from BARB arrived on Tuesday afternoons and carried the full seven-day figures for the week that had ended 10 days earlier. This meant that you would have transmitted two or even three episodes of a new series before you saw any estimate of audience size. The channel controller was flying, if not blind, then in a mist.
Until the second BARB contract in 1991, that is. For it was then that the overnights became available. There were many in the BBC who thought that they were not appropriate for a public service broadcaster - that we should trust our judgement of the quality of a programme and not be rushed into a view based on audience figures.
But programme executives were being paid to make judgements not just on quality, but on likely audience appeal as well. Just as they wanted to know as soon as possible whether or not a new show was as good as expected, so they wanted the earliest possible information on whether a programme had been as popular as expected.
The overnight information was irresistible once you knew it was there. And, while I cannot remember any BBC show being cancelled in mid-run because of poor overnights (though I can remember at least two that were cancelled while still in production in the Eighties because the controller thought they were too poor to keep on the air), they did up the ante. Programmes began to be moved to avoid strong shows on rival channels if the audience voted unfavourably with their remotes. On occasion, shows were shoved out of peak to late slots. Recommissions, too, would be held until a set or two of overnights had passed verdict on a new series.
The competitive position night by night became sharper and more tactical; programme-makers were put under more pressure. Today, Boys and Girls fails to pull an audience on Saturday night on Channel 4 and it is cancelled; Weekend, the BBC political programme aimed at non-wrinklies, is ended after its first series, evidently because of poor figures. This pressure is reflected in the public prints and websites. One minute they call for quality, experiment and ambition, and bemoan the "ratings war". The next, they leap with glee at poor overnights for any prominent show or star.
Minor swings in audience figures over-excite commentators. Last week, we read that the new BBC arts series, Imagine..., "suffered a setback with last night's show pulling in just 1.6 milllion viewers." A "setback"? Really? ITV1's The Vice, meanwhile, was said to have "suffered 'the ultimate indignity'". What was that? It had a smaller audience than BBC1's popular documentary, The Trouble with Sleep.
I guess that the coming of the overnights was both a cause and a symptom of the increasingly febrile world of television. They were demanded by their time, made possible by new technology and fuelled the accelerating competition.
And the next big change? The personal video recorder. It will succeed where the video failed in turning the carefully packaged chocolate box of a controller's schedule into a barrel of pick'n'mix.
Will Wyatt, a former chief executive of the BBC, is author of 'The Fun Factory: a Life in the BBC', published by Aurum Press and priced £20