I feel that starting with the 12 mark questions at the beginning of the examis the best thing for me to do in terms of timing. I realise that I often run out of time in my exams when I don't start with the questions with the biggest marks first.
In my Unit 1 & 2 papers I started off with the 12 mark questions and managed to finish my paper with enough time to look back and read back on the questions and my answers. In both those exams I did rather well. However, I am aware that the Unit 1 & 2 exams are at a lower level than A2, as AS exams don't need as much detail when evaluating a study, theory or research methods.
In my A2 unit 3 Criminology and Child psychology paper I really flopped on timing as I spent too much time on the questions with the smaller marks, and this time I did not start with the 12 mark questions.
Overall, I don't know if this technique applicable to you but I do feel this may help you if you're struggling with timing as it did help me, and this time I will make sure to use this technique for my re-sits and last exams in May/June.