I just finished the game, in about three hours. Although there are rooms I have not inspected like I should have, so I must play again, and I reckon it will be about another two hours.
So yes, you can play it in one hour, if you check almost nothing and reach the attic and pick up the last journal, or you can get lost checking everything for at least 5 hours before you do that. There are interesting secret passages.
Being able to go outside around the house in the rain is the missing part of this game that would truly have made it complete. A shed to explore would have been nice. I like the sound of rain on the roof.
The story is interesting, but the end is shocking. They are vague enough however that you can't be sure exactly what it means. You can decide to believe that it is not as shocking as I imagine it to be.
It is a game worth playing if you have a few hours to kill and if you can get the game at a good price. Indie at heart, but better quality than what we used to have 15 years ago. No big puzzle things, just exploration to discover more of the story of your sister, dad and dead uncle, with a touch of paranormal.
And be ready to use the arrows or wasd to move around, and using the mouse to turn and look everywhere. And don't forget the control key to check under everything, I suspect I missed many journals hiding in some dark corners.
I played it on my Mac using the easy option, I'm not sure if the harder options will make the game that different. I'll try that next time I play.