Need some clarification. Even if there is a long layover, the <72 hours clock starts with the initial leg f the journey, right?

We are traveling DCA-YYZ-DEL (Leaving DCA @1700 on 1/12, connecting in YYZ on 1/13 @ 10 AM and arriving in DEL on 1/14 @ 9 AM).

So, it is 72 hours or less before 1/12 1700 hours, that is test must be done 1/9 1700 or later. Is my assumption correct?

Thanks.