一、这是一个强调句,这里强调的是时间状语,具体结构为——
强调句式：it is ...that
时间状语：at this time
主语：students
谓语动词：realize
并列宾语从句：how much they need to learn and how little time they have to do it.
二、强调句总的结构是——
It is + 强调词语 + that + 其他部分
三、具体应用还可以分为——
1、强调主语：It is + 主语 + that + 谓语动词 + 其他部分.如：
It is students that realize at this time how much they need to learn.正是学生们在这个时候才意识到他们需要学多少.
2、强调其他成分：It is + 强调部分 + that + 主语 + 谓语动词 + 其他部分,如：
It is how much they need to learn that students realize at this time how much they need to learn and how little 学生们在这个时候意识到的正是他们需要学多少.（强调宾语从句）