It is true that when you start to stare at something, or focus on something without being absent minded, your peripheral vision would be lost. This is quite a natural thing. You could regain your peripheral vision right after you stop looking at something. Generally speaking, maybe 20 sec could make your peripheral vision lost.
Yes, it is true that you will lose the peripheral vision when you stare at something too long. And the disappearing time may be about 30 seconds. Actually, our peripheral vision is so weak. Human mainly use the focused vision to see things. Thus, it is the normal state. About the peripheral vision, people could do the eyes health exercise to improve.