The game is still saving automatically after every level. There was too late and no funds to implements that manual save in any time. But If you played early version, then actual version is much much more optimized and has Game Difficulty levels. So for example choosing easy makes that almost every level is possible to finish in 30 minutes.
Great to hear that you played our game already and I'm very happy to see such a post after release game here on itch :)
Best Regards, Let me know if you have any more questions :)
The End of The Sun The Game - http://www.endofsun.com