Complex sentence: Most hormonal birth control pills, especially the progesterone only pill, must be taken at the exact same time each day; a delay of as little as one hour can trigger ovulation and sharply increase the risk of pregnancy.
Split into simpler sentences: Most hormonal birth control pills, especially the progesterone only pill, must be taken at the exact same time each day. An error of even one hour can trigger ovulation and sharply increase the risk of pregnancy.