You can perform these moves at the end of your training to loosen up the tension you have created in your muscles. I am not a big fan of flexibility as a goal in itself as I think it increases the risk of injury if the range of motion is not matched by appropriate strength. I just try to maintain the range of motion required to do the activities I want to do and restore length to the muscles after activities that cause tightness.
Work through the sequence holding the positions for a few seconds each. How long you need to hold is quite individual, find out how long is right for you. The positions needn’t be static and linear, move around a little. Perform around 5 reps of each sequence, as needed.
Follow the stretches in the video by hanging from a bar for 2 sets of 30 seconds. Again, move around while hanging, swing, twist etc.