8½ weeks if counted between the 26 April start of the Beijing-Tianjin test runs and the 24 June record run, 3 months if counted until the opening of the line.

BTW, even in March that year, the design top speed for even the Chinese-built trains was given as:

China-made bullet train to link Beijing, Tianjin in Aug - The Official Website of the Beijing 2008 Olympic Games

The first China-made bullet train designed to run at 300 kilometers per hour has completed a test run and will be in service between Beijing and Tianjin in early August, a railway official said on Sunday.