M23 political leader Jean-Marie Runiga said the delegation had only left the rebel-held DRC town of Bunagana, a border post with Uganda, at dawn on Friday, and were not expected in Kampala until late in the day.
"My delegation...should be in Kampala later this afternoon or evening," Runiga said, blaming the delay on a lack of "logistics" for the travel and stressing that the M23 were committed to talks.
While it is still possible talks could kick off later on Friday, Runiga suggested there would be a delay of one or two days.
"I am not sure when exactly [talks will start]... possibly on Sunday," he added.
Kinshasa's delegation is already in Kampala. Foreign Minister Raymond Tshibanda is leading a team that includes members of the national assembly and senate.
Raft of demands
The rebels' lightning capture of the mining hub of Goma on 20 November, eight months after the army mutineers launched an uprising against the government, had sparked fears of a wider war and a major humanitarian crisis.
M23 fighters, largely from the ethnic Tutsi community, pulled out of Goma last weekend. They are expected to present a raft of demands, including major political reform for the war-weary region.
DRC's president Joseph Kabila, who the rebels have said should step down, is expected to attend a meeting on Friday in the Tanzanian city of Dar es Salaam.
He will join leaders and officials of the 15-nation Southern African Development Community (SADC) at a two-day meeting which is expected to focus on the crisis in eastern DR Congo.
South African President Jacob Zuma arrived on Friday at the talks, Pretoria said in a statement.
The SADC bloc includes nations such as Angola and Zimbabwe, countries that backed Kinshasa during the 1996-2003 Congolese civil wars. It does not include either DRC's eastern neighbours Rwanda or Uganda, who have denied accusations that they are backing the M23 rebels.