when后面可否加上现在进行时.例如：when you're planning a trip ,you shouldn'

当然可以啦.例句：
What do you do when you are having an awful day?
当你今天很不顺的时候,你怎么办?
Always wear your safety belt when you are driving or riding in a car.
当你开车或乘车的时候,一定系上安全带.