London-listed International Distribution Services told markets it would publish its full-year financial results at 7am on Thursday, but by 11.30am nothing had been released.
It comes a week after the company said it was “minded” to agree to a takeover by Czech billionaire Daniel Kretinsky.
Mr Kretinsky, whose EP Group owns a 27.5% stake in the firm, put forward a proposed bid worth about £3.5 billion on May 15.
There have been no further announcements on the deal in the last week, but Business Secretary Kemi Badenoch said the Royal Mail’s universal service obligation will need to be protected in any sale of the firm.
IDS said Mr Kretinsky had agreed to offer a set of “contractual undertakings” to protect key public interest factors recognising Royal Mail’s status as a major part of national infrastructure under the proposal.
This would include commitments to Royal Mail’s plans to keep six-day-a-week first class letter deliveries under the universal service, protect workers’ rights and keep the Royal Mail brand, as well as its UK headquarters and tax residence.
Mr Kretinsky has until 5pm on May 29 to make a firm offer after the City Takeover Panel agreed to extend the so-called “put up or shut up” deadline, which was originally set for 5pm on Wednesday May 15.
Royal Mail, which was privatised in 2013, put forward plans to Ofcom earlier this month to scrap second-class letter deliveries on Saturdays and cut the service to every other weekday as part of overhaul efforts.
In its submission to Ofcom’s consultation on the future of the universal postal service, Royal Mail said it would keep a six-day-a-week service for first-class mail in a climbdown on previous calls for all Saturday letter deliveries to be scrapped.
Shares in IDS were trading 1% down on Thursday morning.
IDS declined to comment.