If I read Kochmann's notes correctly the company was started in 1899 as Deutsche Privat Telephon Gesellschaft by H. Fuld & Co of Frankfurt Germany
They developed telephone systems and later, electric clocks.
In 1920 the European branches were abbreviated, Elektrozeit being one of the chosen names, later further abbreviated to EZ.
In 1935 the whole company was restructured as "Telephonbau & Normalzeit", commonly known as T & N
The production facilities were rebuilt after WW2 and the company was still trading in 1963 using quartz technology