Over the past year as more U.S. consumers have adopted smartphones — more than half of the population now uses one — the number of installed applications is up for both Android(s goog) and iOS(s aapl) devices. Yet the amount of time spent using those applications hasn’t changed much, says Nielsen. In 2011, the average amount of time in apps was 37 minutes per day; a year later, it’s just 39 minutes…

