No idea how many hours, but coming up on 7 years in November. There's a long thread on freegamedev.net chronicling more or less the entire process. It starts off really simple and stupid, and then it just keeps going and going. https://forum.freegamedev.net/viewtopic.php?f=22&t=3710 I'm doing it for free because it's essentially my hobby project. It's fun.