After meeting the obligations of your state in life (work, studies, interacting with family members and friends, household chores, a little exercise, PRAYER, getting enough sleep, giving back to the church or society by some kind of regular volunteer activity, etc.) how much free time is left over?
If it is three hours, it may not be wrong to use that time for video games. Or you might choose to spend some of that time reading, watching TV, playing games, or going on the Catholic Answers Forums.
If you spend that much time on video games every day you may need to prayerfully consider if this is how God wants you to use your time. And also consider what type of video games you are playing.
We can’t tell you one hour is OK, two is venial sin, three is mortal sin. But your question shows you have an idea that three hours may possibly be too long. In my opinion it isn’t a mortal sin unless you are neglecting other duties. Even then, the sin might not be a mortal one. But, of course, if we love God we try to avoid deliberate venial sins as well.
Now here’s a challenge. Lent is coming up. Would you be willing to reduce your video game habit to two hours a day during Lent? Or possibly give up video games once a week? I think God would bless you and by Easter you might have a clearer answer to your question.
Some of us have a tendency to spend that long on these forums and we need to ask ourselves the same question about them…