It depends on where you want to stay(which realm/state) and what you want to do because meditation does affect our physical state and duties. There are people who meditate from half an hour to several days or even months. The meditation becomes 'over' for those who have to fulfill the physical world responsibilities and have a role to play in this realm. The meditation leads to constant peace, a bliss that no one would like to leave and come to this chaotic world. I used to meditate for two hours or more and never wanted to come out of it, just wanted to go on and on. It never used disturb me till I was in that peaceful state. But , when I used to come out of it , I used to find my surrounding extremely chaotic and this used to disturb me as I did not want to talk to anyone, just witness or observe everything peacefully.
Since I work with children, I have to be talking and stay energetic all the time which is completely opposite to what I actually look for...which is staying silent all the time and enjoying the peace. (Fortunately, I am on my break these days, and just loving it).
So for someone like me the meditation over an hour becomes "over" meditation, but for someone like Yogis, mystics, or those who have no worldly duties , the meditation can never become over because they do not have to stay in any world made constraints or frames. They go on exploring the patterns of energy within and out, unfolding the truth and experiencing the bliss. I wish I could be one