There are slight differences in Apple and Google's definition of a Session, which may make accurately comparing across stores difficult.

Session

• A Session defined by Apple is anytime a user brings an app to the foreground of the phone for more than 2 seconds. A session concludes when the user navigates completely away from the app, to the home screen or another app (the app is no longer in the foreground).
• A Session defined by Google is anytime a user brings an app to the foreground of the phone for more than 2 seconds, however, the session is closed as soon as the app launcher is opened. (This typically causes Google to have more sessions, however, the sessions will slightly shorter than Apple's.)

Session Count

The Session Count metric illustrates how often users have a Session on the application per day, week, or month. In the platform, this is denoted in a percentage that shows what percent of users are using the app once a day, twice a day, three times a day, etc.

Session Duration

The Session Duration metric shows the average of how long users are within each Session.

• The first column of Session Duration shows the time period from “0-3 seconds,” however for Apple because a Session must be more than 2 seconds to count as a Session, this column shows Sessions from 2 to 3 seconds in length.
• For Google, this column shows all sessions from 0 to 3 seconds, including 0-2 second sessions.

Time Spent

The Time Spent metric is a combination of the Session Count and Session Duration metrics. It will show the overall average amount of time that the user spends within an application over the selected time period (Day/week/month). This will include the duration of all sessions rather than just the duration of a single session.

Android Session Metrics are only available for All-Time data and data starts Jan 1st, 2020.
Android Session Metrics are only available for apps with over 100,000 all-time downloads.