This article is from the Stretching FAQ, by Brad Appleton Brad_Appleton@ivhs.mot.com with numerous contributions by others.
The best time to stretch is when your muscles are warmed up. If they are
not already warm before you wish to stretch, then you need to warm them up
yourself, usually by performing some type of brief aerobic activity (See
"4.1.1 - General Warm-Up"). Obviously, stretching is an important part of
warming-up before (See "4.1 - Warming Up"), and cooling-down after a
workout (See "4.2 - Cooling Down"). If the weather is very cold, or if you
are feeling very stiff, then you need to take extra care to warm-up before
you stretch in order to reduce the risk of injuring yourself.
Many of us have our own internal body-clock, or "circadian rhythm" as, it
is more formally called: Some of us are "early morning people" while others
consider themselves to be "late-nighters". Being aware of your circadian
rhythm should help you decide when it is best for you to stretch (or
perform any other type of activity). Gummerson says that most people are
more flexible in the afternoon than in the morning, peaking from about
2:30pm-4pm. Also, according to `HFLTA':
There is some evidence to suggest that flexibility and strength are
greatest in the late afternoon or early evening. If this is true, then,
all else being equal, an athlete might get a better workout by hitting
the gym right after work rather than before work.
 
Continue to: