PNF Stretching

Can I get a basic template as to when would be the best times to stretch.

For instance:

PNF before and after speed?
PNF or static after tempo?
Can you use PNF stretches too often? Should you keep it to 3 times/week or less?

Does stretching after speed help aid in recovery by re-lengthening the muscles? or is this a big factor… can you just focus on PNF for tempo days instead?

Thoughts?