Hello, I'm a experienced game developer.
By what you say, I could make some simple assets or I could also find free for commercial use assets or some already purchased assets to make something basic and in that way you can validate the idea.
I think based on your requirements the concept game could be done in 24 days, but it depends on more information we should discuss. Any idea you have, we (You and I) will find the best way to implement it.
I have 5 years of experience using game engines like Unity3D, Unreal Engine, Godot and BuildBox for game development so it shouldn't be hard to be done in any of these. also have experience in software for 3d modeling, illustration and texturing like Blender, Inkscape, Photoshop and Substance Painter.
You'll receive my entire attention and support while the project is in the making and even after the development is done.
I have a lot of experience in game development and I'll do my best to make sure you're satisfied with the results and as I already said, I'll be there if you need help at any moment after the development.
Feel free to contact me if you have any doubt.