I think this is going off-topic, and to reply to OP I'd just say ask your teachers, but I don't think that it's a 'hard' word limit (simply a suggestion).
If you want students to practice writing to time, then tell them to practice writing timed. This is actually quite irrelevant, considering we're talking about a timed outcome anyway here. But in my personal experience, there's actually very little link between number of words and time - I've written over 2000 in an hour before, while I spent an entire day on a 100 word abstract. The less words you have to say what you want, the harder it is to get your point across.
English 1/2 is not supposed to prepare you to university. Its primary objective is to prepare you to English 3/4 which has no words limit (on SACs/exams, at least).