To find this time subtract 7-8 hours before your alarm time

问题描述:

To find this time subtract 7-8 hours before your alarm time
求问这里To find this time是句子中的主语吗?subtract 是谓语?

(If you want) to find this time,(you must) subtract 7-8 hours before your alarm time.
所以在这里To find this time是虚拟语气;后半段的主语是you不过被省略掉了,subtract是谓语.