The so-called inclusive national dialogue aimed at paving the way to restoring civilian rule was given a ceremonial start at the weekend and had been scheduled to start work on Tuesday.
The forum gathers some 1,400 representatives from political parties, trade unions, the government, civil society and armed rebel groups.
It is scheduled to run for three weeks, culminating in agreements to overhaul Chad's institutions and revise the constitution.
But government spokesman Abderaman Koulamallah told AFP "the dialogue has been delayed for organizational reasons, mainly because of the late arrival of certain delegations".
The delay was "not at all for political reasons", he insisted.
"Everything is fine at the moment, the timeframe is good."
If all goes well, the draft constitution will be submitted to a referendum, followed by "free and democratic elections" to enable the return to civilian rule after 18 months of military rule.
One of the world's poorest countries, Chad has endured repeated uprisings and unrest since independence from France in 1960.
It has been ruled by a junta since April 2021, when President Idriss Deby Itno, Chad's iron-fisted president for the previous 30 years, died during an operation to fight rebels.
He was succeeded by his son, General Mahamat Idriss Deby Itno, aged 38.
The forum, his brainchild, should have started in February but was delayed for months as rebels squabbled over whether to attend.
It eventually kicked off on Saturday, although two large rebel groups and a major civilian opposition group are boycotting proceedings.
Saleh Kebzabo, a senior member of the organizing committee and former opponent of the elder Deby, said that work this week would "focus on adopting internal rules" for the talks.
Thereafter, commissions will start work on August 30, focusing on individual themes, such as social issues, peace, national reconciliation and fundamental liberties.
The initial schedule has a closure ceremony for September 20.
"The length (of the meeting) is not imperative -- if it needs more days, we will take more days," said Koulamallah, who is also communications minister.
The 18-month "transition" set by the junta runs out in October, which leaves scant time for organising a referendum and elections in a vast underdeveloped country.
Deby, who has the title of transitional president, gave himself the option in June 2021 of extending junta rule by 18 months if need be.