Currently, the information is sent out to broadcasters at 6am, five hours before it is released to the press and public and before the Stock Exchange opens.
Despite there being an embargo on the data until 11am, when the top-line audience listening figures are officially presented, subscribers believe there could be an opportunity for the system to be abused prior to the public release.
Capital, Emap, Chrysalis and GWR own the main commercial radio stations and leaked audience figures could be detrimental to their share prices in the volatile market leading up to the results.
Under the new method, subscribers will receive their audience data at 5.30pm on the eve of the release date.
The figures will then be embargoed until 7am the following morning, when the media and the City will be made aware of the top-line situation.
A press conference will then be held at 9.30am.
Although there is no definite evidence of the system being misused, officials at the radio body believe circulating the information the day before general release will give companies more time to prepare press releases.
Jenny Abramsky, the Rajar board director and director of BBC radio and music, said: "We recognise how important the timing of the release of data is for the commercial sector and we are, therefore, happy to support this change."
The changes will take effect from the next Rajar release date, which is due on Thursday October 21.
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