Low back stretches are important to recover from back pain. I recommend knee to chest stretches for most conditions.
The knee to chest stretch opens up the lower spinal joints which promote blood flow and synovial fluid circulation in the joints.
Stretches also stimulate the mechanoreceptors which help block pain signals travelling from the area to the brain.
I usually recommend stretches at 2-3 weeks into care. The top priority with a new client is to help reduce pain and start the healing process.
Every person is different, so please consult with your health professional before starting any stretches.