in the same boat as you. in the trails i stopped at 40 mins with 1 paragraph of the 5 marker done. moved onto my creative which i had memorised and got down in 30 mins and had 10 mins to go back to short answers.
i deff know i over answer the questions but i get paranoid i havnt so i keep writing...
How long you spend on a question should be based on how many marks the question is worth. 2 mark questions i generally write 1-2 paragraphs on and 4 mark questions about 3-4. It also depends on what the question is asking, if its a basic: 'describe one technique utilised' then definitely watch you don't over answer.