This is the 72nd most frequent Japanese word.
くらい
"くらい" (kurai) means "about," "approximately," or "around" when indicating quantity, and "degree" or "extent" when showing level or comparison.
Here, くらい indicates an approximate amount of time, showing about how long something takes.
一時間くらいかかります。
It takes about an hour.
In this context, くらい expresses the degree of something, suggesting it was so good to an extent that it was almost frightening.
この映画は怖いくらい良かった。
This movie was so good, it was almost scary.
Here, くらい is used as 'at least,' implying that as a minimum action, students should clean their rooms.