"What are you planning to do during the break?"
你 should be able to go before the time phrase. (Currently it's not allowed.)
Not necessarily so for "打算", in my experience. A time phrase/word can go after "打算", particularly if you're answering the question of when you plan to do something, as opposed to what you plan to do at a given time:
A Google search of "打算明天" returns about 350,000 results, with a common context being "我打算明天 + V".
And the following grammar book has several examples of "打算" coming between the subject and a time phrase:
If you're answering the question of when you plan to do something, as opposed to what you plan to do at a given time, "打算" can certainly come between the subject and the time phrase.
Examples in a book on Chinese grammar:
"X 的时候" is "when X is happening".
时间 is typically about duration, i.e. how long something lasts or has lasted, or having or not having enough time, or the clock time (in general or in relation to the occurrence of an event), whereas 时候 is about the point time when something occurs or the period when it's occurring, without reference to its actual clock time or duration per se.
Perhaps it's not impossible to say 时间, but it may suggest something like "how are you going to use your vacation time effectively". I'd like to get a native Chinese speaker's take.
This lesson is utterly hopeless with respec to the accepted renderings of 'during'. Sometimes they want 的时候, sometimes 在, and sometimes nothing at all beyond the word for 'break'. There is no logic to their choices, and most of the time DL accepts only one as correct. Very frustrating.