Question

When从句是前提条件还是主句是when从句的条件，就逻辑上when从句是引导主句的吗？还是相反的

Answer 1

when引导的是时间状语从句，是从句，谓语动词的发生时间可能与主句谓语动词时间是同时发生，也可以是提前的，也可以是之后。
when she saw his friend, she was singing.同时
when she arrived, her mother had cooked supper.之后
when she comes, please tell me.之前

Answer 2

when从句是主句的前提条件，就是说when从句是时间从句有动作或状态时，主句才会……。
When you come, she will leave.
你来时，她才走。