Where to find the nightly build source files?

So I am new to this world, and having fun, but I have an ender 3 pro with 4.2.2 board and cr touch. I downloaded and installed
https://marlin.crc.id.au/ (use the Ender 3 - v4.2.2 Board - BLTouch)

And it works great, but I want to make a few changes, like enable remaining time and % complete.

I thought with the bin file, there would be the source for that bin and I could make my changes and build it, but they are not there.

Do I have to star from scratch? I see in the description of this firmware it lists what was done, but not sure I understand it all and don’t want to screw something up.

Are the source files for these bins anywhere?

The source for these builds comes from:

The base configuration for the Ender 3 is here:

where can you get the nightly build source files instead of starting from the base files?