I cannot say how long you would need to learn to code. But if you want to see how long it would need to write your own Poser or C4D, well - take a look at Silo 3d. It's done by two people full time. Download the software have a look.

Silo 1.0 was released 2004, I have no idea how long they were writing on this. But the changes for 2.0 took years for two programmers. That's just the modeler.

Packages like Poser and Cinema 4D include a renderer too. A rigging system. Scripting. See how long DAZ needed to create Studio.

You may learn coding and try to expand existing software like Blender. But I think to create a package like Poser you would take years, and decades for a full blown package like Cinema.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.