Last week, Sir George Russell, chairman of the ITC, wrote to them saying they would be in breach of their licences if they went ahead.
Until Sir George's intervention - backed by the Prime Minister and the Leader of the Opposition - the change was expected to be confirmed at yesterday's regular meeting of the chief executives of the 15 companies.
But after the meeting they said they would 'explore fully with the ITC the differing interpretations of the 1990 Broadcasting Act in relation to the scheduling of the high-quality news service to which ITV remains completely committed'.
This discussion is likely to take place a week tomorrow.
In last week's letter, Sir George said that because some of the companies had given a specific commitment in their franchise applications to schedule the news at 10pm, and because they were all obliged to show it at the same time, there could be no change without his agreement. The companies, however, believe that the only binding commitment they made was to show the news in peak time - between 6pm and 10.30pm.
The difference in interpretation means that the matter could end in court.
Sir George's letter did not rule out change, but suggested that it might be inappropriate so soon in the life of the new regional Channel 3 licences.
Yorkshire-Tyne Tees, the fourth-biggest ITV company, is to axe 188 jobs as part of a cost-cutting drive. Nearly 300 jobs went at the company last year following the pounds 30.4m takeover of Tyne Tees by Yorkshire.