"What are you planning to do during the break?"
你 should be able to go before the time phrase, I believe. (Currently it's not allowed.)
Could anyone explain to me why 放假的时候 doesn't go in between 打算 and 做?
Or before the verb: 你放假的时候打算做什么？ But with modals (or similar words like 打算) it has to go before that modal, not between the modal and the “main verb”.
I'm not sure that's always true. I think a time phrase/word can go after 打算, particularly if you're answering the question of when you plan to do something:
A Google search of "打算明天" returns about 350,000 results, with a common context being "我打算明天 + V".
Of course I'm open to correction, and would certainly defer to a native speaker.
Let me give a simple dissection for some sentences with the same meaning without considering their nuances:
- 明天 我要去香港 = tomorrow + I will go to Hong Kong
- 我 明天要去香港 = I + will go to Hong Kong tomorrow
- 我 要 明天去香港 = I + will + to go to Hong Kong tomorrow
You can see how tightly the time phrase 明天 is associated with different parts of the sentences. We should tell the suitable positions by analyzing the sentence structure. (not easy to explain it to beginners ;-)