It really just depends on too many factors to give a straight answer.
Let's start with something simple - writing. Depending on your expertise, how fast you write, and how many edits you do, it can be anywhere from 100 to 1000+ words an hour of writing. If you're stuck on a tough scene, it can be significantly longer; I've had days where I work for sit there for 10 hours to maybe get 500 words done, if that.
When you get into backend Renpy code... it can be 30 minutes or 8+ hours to get some coding functionality done, again depending on how much experience you have and your talent/skill for coding. And the more complicated your game, the more bits of functionality you need.
If you're doing full on RPG or sandbox stuff that requires actual Python or another coding language, it's hard to give any kind of meaningful estimates, because it depends on so many factors. Using a premade engine vs making your own, planning out HOW to handle aspects of the battle system, etc. But you should expect a *lot* of hours for a polished system.
Planning things out doesn't get much attention, but it's crucial to having meaningful character arcs, plots, battle systems, etc. and takes a lot of time to do properly as well. Not all of it has to be dedicated time - sometimes just ruminating on an diea while doing other stuff is fine - but even in your downtime you'll often end up thinking about the game. I know I do lmao.
Depending on if you're doing your own renders or commissioning content, that can add a LOT of extra time - the more detailed your commissions, the more work you put into finding good references, the faster that time investment balloons out of control. And if you're doing commissions, going back and forth with the artist can take a surprising amount of time, sometimes interrupting your other workflow. Can end up taking a few days on your end for a higher-quality sprite, and a lot more on the artist's end.
To say nothing of my experiences trying to fix bugs or implement new features without breaking spaghetti code, and then fixing that code to not be shit.
For some perspective, my game has around 20 hours of playable content, maybe 25 if you're a slower reader. I've put around 3000 hours into making that. I was a complete amateur coder, had to make the rpg engine from scratch, and had to fix a lot of things I did poorly or incompletely the first time around. And I'm a pretty fast writer when I get in the zone, but it's easy to get stuck on a scene, and learning how to commission well took a lot of time too.
I put in somewhere around 30-60 hours a week, sometimes approaching 70. On a good day, I'll get 6000 words done. But there are a looot of days where I end up getting little or no writing done because I had to deal with some other aspect of the game.
Even if you're 'just' making a kinetic novel with no mechanics/choices whatsoever, it can still take a long fucking time. One of my closest friends is working on a (non-porn) kinetic novel of his own, he writes fast, has the whole damn thing planned out, dude's a straight-up workhorse, and he's still put (very rough estimate) around 800+ hours into making around 10 hours of reading for the first, like, 1/4 of his story.
As woody said - take the worst-case scenario and multiply it by 10 to get a rough idea of how long it'll take if everything goes well.