The document below was issued by EASA some time before December 2012
AMC1 FCL.025 Theoretical knowledge examinations for the issue of licences
(e) ‘Sitting’: a period of time established by the competent authority within which a candidate can take an examination. This period should not exceed 10 consecutive days. Only one attempt at each examination paper is allowed in one sitting.
The new Standards Document 11, which included the material below was issued by the UK CAA in December 2012. So we can assume that it is the UK CAA interpretation of the EASA document.
"A sitting for the PPL and LAPL is defined as the attendance at an examination centre for the purpose of taking or writing a single or set of examinations in one day."
The UK CAA "One day" definition is within the limits set by the EASA "10 days" definition, so it conforms with the new rules.
As Beagle says, a sitting can be up to 10 days...so the whole sittings thing becomes a bit meaningless.
That is true only if the competent authority has established 10 days as their definition. But the UK competent authority (The CAA) has selected one day as the duration of a sitting.
I suspect that this will turn out be like so much of the other material in the standards documents....the CAA will publish it, but they will take on action to enforce any of it.