i try to stretch at least 7+ times a week. mostly my legs get all the attention, as they are tight compared to my arms and torso. i warm up and stretch lightly before a workout, and then stretch deeply after the workout to cool down and relax the muscles. i stretch before any sort of gymnastics as well, 2 nights a week.
after work would be an excellent time to stretch if you cannot stretch directly after a workout. since it is later in the day, your muscles are more pliable as well. it would make a very good way to relax after work, too.