In fact, travel apps saw the highest increase in time spent -- increasing 40%, from one hour and 28 minutes per person to two hours and three minutes -- from the fourth quarter of 2014 to the fourth quarter of 2015, according to Nielsen.
During the period, home and fashion apps saw the highest increase in unique audience, as they grew 73%, from 30.2 million to 52.4 million.
Entertainment and search, portals, and social networking remained the largest app categories, with more than 165 million unique users each.
Mobile commerce also gained in popularity, as the commerce and shopping category eclipsed 125 million users who averaged two hours and 48 minutes per person throughout the holiday season in fourth-quarter 2015.
More broadly, smartphone penetration across the total U.S population for adults 18 and older increased to 74% (81% of mobile subscribers) in the fourth quarter of 2015.
During the period, smartphone owners used an average of 27.1 different apps per month, according to Nielsen.
Despite rapid evolution throughout the marketplace, including new apps -- additional device functionality and broadened device capabilities -- the number of apps used has remained relatively stable since the end of 2012.
While there appears to be a limit to the total number of apps people actively use each month, the time they spend engaging with those apps continues to grow steadily.
Since fourth quarter 2012, the time spent per person each month has jumped from just over 23 hours to almost 41 hours -- an increase of 77%.
Meanwhile, the average time spent per app has also grown during the period, increasing from 52 minutes in fourth-quarter 2012 to one-and-a-half hours in fourth quarter 2015.
Overall, women use slightly more apps per month than men do, and they spend almost three more hours using them. The average time spent per app, however, is relatively even for men and women (1:33 for females and 1:27 for males).
When it comes to age, smartphone users between the ages of 25 and 49 are most likely to access a variety of apps, but the heaviest users by times spent skew slightly younger.
Millennials age 18-24 access relatively fewer apps (25.6), but spend nearly two full days per month using them, while users 25-34 spend 46:31 on 28.2 apps.