From 12:00 p.m. to 3:00 p.m., I taught my intro class, 3:00 p.m. to 6:00 p.m., I taught my advanced class.
De 12.00 p.m. a 3:00 p.m., estuve dictando mi clase introductoria, 3:00 p.m. a 6:00 p.m., dicté la clase avanzada.