I'm impressed by the speed and frugal resources with which they implemented the site and the project has obviously been a huge success, but it is not true that it all had to be completed on that timescale. The release of the MP's expenses has been expected for months, if not years. A delay to the launch of the site would have invoked the 'isearch' law of project management:

"The worst delay to the completion of any project is the management decision to start the project."