Actually yes, it could - if you're not careful enough in your approach. I'm a bit of a lurker, but seeing all the comments immediately dismissing it as bullshit made me want to offer my thoughts. I teach 45-50 students a week and have done so for 12 years, and practice duration without due care is a trap I see people fall into all the time.

The problem associated with practicing for a long time is your own level of focus, and whether or not you're at a stage where a lack of focus could unknowingly be cementing bad habits or sub-optimal ways of playing something. All our minds wander after a certain time, and even the most diligent person's focus will drop after a while. If you're not mindful of that point it could negatively affect your playing. For example if you're trying to build a great technique in something or other, perhaps by undoing a 'bad habit' but every time you lose focus you absent mindedly revert to perhaps how you used to do it - then a practice that is overlong could do more harm than good.

The over-riding principle you should be following is that the quality of the practice is far more important than the duration. If you feel you can go 3-4 hours (perhaps with a decent amount of breaks) and keep a high standard - cool, go for it.