12- When/how long/...for / since

Compare When + past simple / and How long + present perfect

John - When did start raining?
Peter - It started raining an hour ago at 1 o'clock.

John - How long has it been raining?
Peter - It's been raining for an hour since 1 o'clock.

_-------------------------------------------------------

John - When did Anselmo and Suzana first meet ?
Peter - They first meet a long time ago when they were at school.

John - How long have Anselmo and Suzana Known each other?
Peter - They've known each other for a long time since they were at school.

_ ------------------------------------------------------

* Weuse both for amd since to say how long something has been happening.