This was my DDs least favourite type of question. She could do them but they took absolutely ages.
You can only speed up to a certain extent. We decided hat the best thing would be to leave them until the end and do questions that took less time first. She practised hem a bit to improve speed and accuracy. The important thing to know is they tend to be guaranteed marks as long as they see the pattern and with practise they should.
Then the other thing DD decided to do was not to necessarily do them in the order given. (Forgive me if I explain this badly, it's been a while)
Firstly she tackled all the codes that went one way, then all he ones that went the other, so the brain isn't trying to flip from one to the other. This made a big difference.
Luck on the day, they didn't come up.