How to plan this mission?

I need to fly out as long as possible along the track (think a line) between mission item 7 and 8.
Then return 50m south of said line.

I wish to see the estimated flight time.
If I change mission item 6 - to be a delay or something, then a line between 7and 8 will be drawn, and I can align the line between 2 and 3. but at the same time, the flight time will include the “helping lines” 7,8.

Is there a way that I can see the line between 7 and 8, but not take it into flight time calculations?

It would be nice to have the option to have non-mission markers or lines to help plan some type of missions.

You can make overlays for Mission Planner in Google Earth or any other editor that supports .kml export. There may be option to load KML files in QGC too.