1) New material is explained at every lesson.
2) New material is being explained now.
3) New material has been being explained for 10 minutes since 9 o'clock in the morning. - Но это очень сильно притянуто за уши, так как даже не все лингвисты соглашаются, что такая форма (Present Perfect Continuous Passive) допустима.
4) New material was explained yesterday.
5) New material was being explained yesterday at 10 o'clock.