That graph is very misleading. It shows both valves being open, but it doesn't say how much they are open. At the end of the valve travel, 10° of camshaft rotation moves things only a fraction.

Some may be led to believe that there is a time when the valves are both open substantially. If anyone needs an illustration of effects of having a valve open more than a crack when the piston is a top dead, they need to get around an engine that had the timing chain slip. Such will result in bent or broken valve stems & push-rods. Sometimes a push-rod will even punch a hole in the stamped rocker arms too.