The Talmud (Berachot 6b) says, "A person should always be scrupulous about the Minchah prayer." The special quality of Minchah is that it comes in the middle of the day, when people are occupied and busy with their personal affairs, yet they interrupt these to pray to G-d.
R. Schneur Zalman of Liadi (Hayom Yom, 22 Adar I