I downloaded some clips from a game and they are webm files. I tried to put a timer om each clip but I noticed that my times were not the ones I saw on the game, they area a few decimals of a second off. I tried to see the frame rate of the original files but it doesn't say. This being said, can the app change the time of the video? Can I do anything to resolve this?

It usually doesn't, but it might be 1 or 2 frames off if you're not using the same framerate in your project as your files do. You can check that in their properties in kdenlive. Usually though, when you first import your files, a prompt will show up asking if you want to change the project's settings to that of your clips.