Nope, I don't have any links. Just a generalized article...
In reality you want to stretch as much as possible.
You will be sore initially so aim for 3-4x a week at first.. then can go to everyday once you start not getting as sore.
2-3x a day if possible... 3-5 sets per exercise of 20-30s hold or as far as progress lets you before you terminate the sets.