In Ramaswami's book The complete book of Vinyasa Yoga, the postures above come after Dakshina bhairava asana on the right side in the previous subroutine (day 63) but then then appears again after yoganidra along with a both legs taken to the side variation.
It can of course stand as a subroutine in it's own right and is an excellent twisting posture.
Ramaswami has other variations of the sequence where the legs are together.
In one variation, you take your legs up and over to the side to land on your palm in one movement, stay for three to six breaths and then return to asana sthiti and then repeat on the other side.
In another variation you take the legs up and over to the palm on one exhalation return to asana sthiti on the next inhalation and then take to the other side on the next exhalation. you can then repeat the vinyasa three to six times, resting between movements if you become short of breath.
Raise the leg(s) from the hip rather than from the foot and lower leg
Press the length of the arm(s) into the mat to give stability.
Lift the head slightly before turning the head
Twist at the hips
Try to keep the back flat.
Ideally the trailing leg should remain as flat and straight as possible, this is challenging.