Can't say what you're asking about here, as BMX bikes aren't used in a velodrome.
The construction of the velodrome for the 2012 London Olympics took approximately 14 months. Groundbreaking began in early 2010, and the venue was completed in early 2011. The project involved significant planning and design to create a state-of-the-art facility for track cycling events.
It took approximately 6 years to build the London Eye.
the olympics are on for 1 month in the summer in england london 2012
balls
About one year.
How long did it take to build st James cathedral london
July 27 2012 until August 12 2012
1886 to 1894
Eight years
About six years.
1886 to 1894
17 days