The Earth rotates on its axis once every 24 hours. (Well, actually a little less, by about 17 minutes, but close enough.) That's $360^circ$ in 24 hours, or about $15^circ$ per hour. $15^circ$ is 30 times the width of the Sun or Moon. The Sun moves exactly that fast (on average), the stars a smidgen faster, and the Moon a tad slower. (The Moon lags behind the stars by approximately its own width every hour.)
Since Venus is never more than about $45^circ$ from the Sun, it always sets at most 3 hours after the Sun does, and rises at most 3 hours before.
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