The talks were initially scheduled to start Monday, and any further delay could dash hopes of ending Yemen's war after the fugitive government delegation threatened to pull out if meetings did not begin immediately.
"According to the latest information, the rebel delegation should arrive in Kuwait by the end of the day," said one diplomat close to the talks, referring to Hothis.
"As a result, the talks could be delayed further until Friday," another diplomat said.
On Wednesday, UN spokesman Stephane Dujarric said negotiations would begin in Kuwait Thursday.
The Houthis only agreed to join the talks after they said they received assurances from the United Nations that forces loyal to Yemen's former fugitive president Abd Rabbuh Mansur Hadi would respect a ceasefire which has been violated by the forces since it came into effect on April 11.
There was still no word Thursday from the Houthis on their expected time of arrival.
Representatives of the movement and their allies left Sana'a Wednesday for Oman and they are expected to continue on to Kuwait.
But they were still in Oman Thursday morning, according to diplomats.
The talks are the most important attempt yet to resolve Yemen's devastating conflict, which the UN says has killed more than 6,400 people and forced almost 2.8 million forced from their homes.