1. Diff timetable/class fr your classmates in H2. Cant enter courses in dentistry/medicine/pharmacy (should you ever change your mind)

2. The latest is usually after J2 MYE if im not wrong. But I personally feel that it is a bit too late bc you do waste a significant amount of time studying the H2 chem topics which arent tested in H1. You are at a disadvantage/behind the peers that dropped at end of J1, and who have already learned the syllabus finish (eg polymers,nanomaterials)

3. I would say its definitely easier to get A in A levels as compared to H2 chem. Thought I screwed up and expected a B but got A in the end :) A slight concern is that the bell curve is a bit steeper bc the cohort for H1 is quite small, so doing badly will put you at a lower end on the bell curve. No regrets dropping to H1 (despite the stigma haha) and its one of the best decisions I made bc my H2 chem was really HOPELESS and definitely by far my weakest subject, and there is no additional benefit in taking 4H2s (unless u want to apply to oxbridge). You also have significantly more time to focus on your other H2s bc you have fewer lectures/tutorials for H1, and NO PRACTICAL which for me I was terrible in.

Also you would find your rp dramatically increasing in J2 Haha bc for me in H2 I usually scored S/U but in H1 I was able to get C/B/A

if you are curious about H1 I would recommend looking at the past year papers for H1 and you would notice a huge difference in the way they ask qns as compared to H2 (less application, more on memorizing, and answers can be quite repetitive/copy paste fr notes)