Systems, methods, and computer-readable storage media for optimizing and reporting time spent by a user engaged in a session. The system first obtains data associated with a presentation of an item of content at a mobile device, the presentation being divided into multiple partitions. Based on the data, the system adjusts at least one respective length of time associated with the multiple partitions to yield at least one adjusted length of time, the at least one adjusted length of time reflecting estimated time of user engagement with content associated with at least one of the multiple partitions. The system then determines an amount of time spent by a user at the mobile device engaging in the presentation based on the at least one adjusted length of time and the multiple partitions.