Retrogrades

Mercury - 3 weeks at a time, once every 4 months
Venus - once during 584 day synodic cycle, 6 weeks approx.
Mars - 9 to 10 weeks, 6 months of 26 month cycle (25% of cycle)
Jupiter - every 13 months for 4 months
Saturn - 4 1/2 months out of 12 1/2 month cycle