I follow these steps and now Ian and Lena get into a relationship in chap 9 and not later in the game in chap 12. How can I prevent them from getting into a relationship early?
Hmm this is tricky. I suspect EK was a little bit too eager with the combination of early restrictions and late game Jeremy drama, and as a result it's really hard to find a way to navigate between these.
About the only option i can see in the script is to have Ian get involved with Alison and, earlier in Ch.9 during the trip with her, to pick the love options: "Embrace her" and then "I love it too". Having the love flag active blocks Ian from starting relationship with Lena later in Ch.9 and they can instead agree to keep it casual. Then, early in Ch.12 it is possible to respond to Alison's text with "I'm busy" which breaks the love flag.
This, in theory, should allow Ian to get together with Lena later in Ch.12, but keep in mind this is all theoretical and untested.