Time period was a term which refered to different points in time.
Visting Shoreditch November 1963 with Ace, the Seventh Doctor observed that her clothing and tape deck were anachronistic for the time period. He later noted that the aerial of a van used by the Intrusion Counter-Measures Group was a very sophisticated piece of equipment for the time period. (TV: Remembrance of the Daleks)
Martha Jones advised the Tenth Doctor to take care in the future and the past "and whatever other time period you find yourself in." (TV: The Lazarus Experiment)
The Thirteenth Doctor found that the Kasaavin had embedded themselves in multiple time periods on Earth. (TV: Spyfall)