It is not that exact for everyone.
Symptoms may appear anywhere from 2 to 21 days after exposure to Ebola, but the average is 8 to 10 days.
http://www.cdc.gov/vhf/ebola/symptoms/index.html
I understand symptoms can appear 2 - 21 days after exposure. Maybe I misread this chart, I thought this is a chart of how the disease progresses. Am I wrong??