It was/will be+时间段/long+before... It be+时间点+when... It be +时间段+since... “自从.......已经有多长时间了” It is almost five years since we saw each other last time.(主句用一般现在时或现在完成时） 自从上次我们见面以来已经将近五年没有见了。 -- Did Jack come back early last night? -- Yes.It was not yet eight o’clock when he arrived home.（主句谓语动词可以是一般过去时，也可以是一般将来时） It won’t be long before we get used to the new school life.