The deadline for English training contracts commencing 2019 is often July 31st, although some are earlier, and some later. You will find lots of online lists – I quite like this one from The Lex 100:http://www.lex100.com/index.php/career-clinic/deadlines/training-contracts
The 2 years in advance allows you satisfy requirements (conversion course and LPC)before embarking on the training contract.
Students who have studied an honours degree at Edinburgh (any discipline) will be expected to take a conversion course followed by the LPC before embarking on a training contract. The Graduate Diploma in Law allows non-law graduates who want to qualify as either Solicitors or Barristers to satisfy the professional body requirements of the academic stage of training for Solicitors and Barristers. Even those who have studied an LLB here will undertake a conversion course (to cover the required English law subjects) but with some exemptions and the possibility of distance learning and online formats.
For more information on training to become a solicitor through the English jurisdiction use the Careers Service webpages here.