The term described for elapsed term during a chapter. In Easy Mode, there are 16 periods, in Normal mode, there is 24, and in Hard, there is 28, per chapter. Depending on the mode, Spiritual Concentration, visiting towns, and beating dungeons may take up Periods. An example being; when you visit a town, you are using 1 period. Most dungeons require 2 periods. Once all your periods are up, then that chapter is over, and Sacred Phase begins. This means you have to budget your time wisely.