It is four months to go until the secession referendum in South Sudan, and the United States, one of the main brokers of the peace deal between north and south, is showing concern that all goes well.
President Obama is to attend a special meeting on the issue at the United Nations later this month.
Meanwhile, his Secretary of State Hilary Clinton has been speaking frankly to experts at the Washington-based think tank, the Council on Foreign Relations.
She was responding to a question by Travis Adkins, a international affairs fellow with the Council on Foreign Relations.
He explained to BBC Network Africa's Audrey Brown why he thought Mrs Clinton made the "time bomb" comment.