"The airport authorities tell me it will be Monday night or very early on Tuesday at around 1 am," Lewis Brown told Reuters by telephone on Sunday.
Nancy Writebol, a missionary working for U.S. charity Samaritan's Purse, is due to travel on the same plane that transported her colleague Dr. Kent Brantly from Liberia on Saturday, Brown added.
The plane is equipped to carry just one patient at a time.
Meanwhile, an American doctor stricken with the Ebola virus while in Liberia and brought to the United States for treatment in a special isolation ward is improving, the top U.S. health official said on Sunday.
Dr Kent Brantly, a 33-year-old father of two young children, was able to walk, with help, from an ambulance after he was flown on Saturday to Atlanta, where he was being treated by infectious disease specialists at Emory University Hospital.
"It's encouraging that he seems to be improving - that's really important - and we're hoping he'll continue to improve," Dr. Tom Frieden, director of the U.S. Centers for Disease Control in Atlanta, said on CBS's "Face the Nation".
Frieden told the program it was too soon to predict whether Brantly would survive, but said it was unlikely that Brantly's wife and children, who left Liberia shortly before he began exhibiting symptoms, had contracted the disease.
People who are exposed to Ebola but are not sick cannot infect others, Frieden said. Brantly, who works for the North Carolina-based Christian organization Samaritan's Purse, had been in Liberia responding to the worst Ebola outbreak on record when he contracted the disease. Since February, more than 700 people in West Africa have died from the infection.
Ebola is a hemorrhagic virus with a death rate of up to 90 percent of those who become infected. The fatality rate in the current epidemic is about 60 percent.
Despite concern over bringing Ebola patients to the country, the CDC's Frieden said the United States may see only a few isolated cases in people who have been traveling.
"I don't think it's in the cards that we would have widespread Ebola in this country," he said.
The facility at Emory chosen to treat the infected Americans, set up with the U.S. Centers for Disease Control and Prevention, is one of only four in the country with the ability to deal with such cases. The two Americans will be treated primarily by a team of four infectious disease physicians, and will be able to see relatives through a plate-glass window and speak to them by phone or intercom.
CDC spokeswoman Barbara Reynolds has said the agency was not aware of any Ebola patient ever being treated in the United States previously. Five people have entered the country in the past decade with either Lassa Fever or Marburg Fever, hemorrhagic fevers that are similar to Ebola
The U.S. Food and Drug Administration said on Friday the agency stood ready to work with companies and investigators working with patients in dire need of treatment.
A senior official within the FDA said the agency would consider providing treatments under special emergency new drug applications, if the benefits of the treatment outweighed potential safety risks.