"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

"A 21 day period for quarantine may result in the release of individuals with a 0.2 – 12% risk of release prior to full opportunity for the incubation to proceed."

http://currents.plos.org/outbreaks/article/on-the-quarantine...