Yes, there is even a European Convention on the Calculation of Time Limits. And yes, Theresa May, the Home Secretary, acting on poor advice from government lawyers, appears to have misunderstood it. The Convention was drawn up in 1972 by the Council of Europe “to achieve a greater unity between its members, in particular by the adoption of common rules”. It defines the dies a quo and dies ad quem – the start and end of any time-limit.