These poses are meant for Iyengar students who have already been taught how to safely enter and exit them.
The duration that you hold each pose is individual. Aim for 30 seconds for each pose (or for each side if it is a two-sided pose), but bear in mind that how long you hold a pose is very individual. If you find that your body shakes or there is strain, it’s time to come out. If any pose causes you pain, come out of the pose and skip it. When you return to class you and your teacher can work together on how to adapt the pose to resolve the pain.