时期(shí qī) - period, phase, era in Mandarin

时期 (shí qī) is a stretch of time treated as a unit with a character of its own: a historical era, a stage of a life, a phase a country or a company goes through. It is the word behind 困难时期, a difficult period, and 抗战时期, the war years.

It behaves like a time word, so it can sit at the front of a clause as a setting: 那个时期，什么都很贵. When you want to name the period explicitly, the pattern is modifier plus 时期, as in 学生时期 student days or 这个时期 this phase.

The trap is using it where English says "time". 时候 is the everyday word for when something happens (我小时候, when I was small), 时间 is time as a quantity you have or lack, and 时期 is a named span with a shape to it. 我没有时期 is meaningless; you want 我没有时间.