Navigation based on date/time (New Mission)

Continuing the discussion from Time Stamped GPS Coordinates:

Hi, everyone! Thank you for your help!

I wanna create the new mission which is that a vehicle move base on date/time.
This topic was previously posted and I think @RagnarRainMaker 's idea is so great.
However I don’t know which directory and which code I should research and how to define new variant because I’m a beginner.

In the first place, which should I change code QGC or PX4/Firmware or both?

:sob: :sob: :sob: