The easiest way to do this without having to nest footage or calculate an offset, is to create a Transparent Video clip with the timecode effect on the clip and place it on the highest layer above all your clips.
Go to File > New > Transparent Video.
Place the Transparent Video clip on your timeline in a new layer above all of your other footage and extend it for as long as you would like the timecode to appear.
Select the clip, and from the Effects pane, drag on the Timecode effect.
Change the Source dropdown to 'Clip' and your timecode should match up with the whole sequence.