Student or Learner
Would you check the below sentences?
The movie had already started when we arrived.
The movie had already started before we arrived.
Can we use both "when" and "before"? If we can, is there any difference in meaning?
Or can we use only either of them?
My teacher(from U.S.) says he would use "before", not "when" in the above case.
I apprecaite your help.