Hazrat Jabir says that Zuhr is as its name suggests. Asr should be offered when the sun is bright and shining. Maghrib is also as its name suggests. We used to offer Maghrib prayer with the Messenger of Allah (peace and blessings be upon him), then we would reach our homes at a distance of one mile, and even then we could see things at the distance of an arrow's throw. The Prophet (peace and blessings be upon him) would sometimes offer the Isha prayer early and sometimes delay it. Fajr is as its name suggests, and the Prophet (peace and blessings be upon him) used to offer it in darkness.