When a transfer student falls behind in English, the usual advice is to read and write more. That is not wrong, but it does not tell you how large the gap is, nor when it will close, and so it tends to become a long, vague anxiety. The better first step is to quantify the gap.
Measuring it is straightforward: take a graded word list, quickly mark which words you know and which you do not, and you get a rough estimate of your vocabulary size. Compare that with what the target year group typically requires and the gap changes from 'a lot' to 'roughly N thousand words'. The number does not need to be exact, but without it no schedule can be built.
What matters is that English in Hong Kong schools is assessed less as everyday conversational vocabulary and more as academic usage: long sentences in argumentative and explanatory writing, abstract nouns, subject-specific terms. So the catch-up material should be academic vocabulary and reading comprehension, not more conversational phrases. Get the direction wrong and the hours will not show up in school results.
When scheduling, twenty to thirty minutes every day for six months beats four hours at the weekend. Vocabulary retention depends on frequency of exposure, not only total time. Adding one short piece of writing a week, in which you deliberately use the new words, makes them stick far better than drilling lists alone.
One last thing: do not run three textbook series at once. Switching materials means restarting each time and progress feels stalled. Finish one graded series before starting another.