Use The Flow Builder to build a session with 30-minute timeout from inactivity. Count the number of sessions in the last 7 days.
Open the Flow app. Build a Session (Flow) that is one step. You can remove steps 2 and 3 by pressing the - button in the top right of each panel (see image below). Step 1 should start flow on all events. The bottom section of the Flow builder in the Global Rules set the rule to end flow from inactivity of 30 minutes. Name the Flow and save it.
The Flow App is fundamentally a Session builder. Scuba thinks of Flows happening inside a Session. A Session can include any and every action (filtered to all events as one step), or it can follow a structured sequence of events if needed. The Global Rules portion at the bottom is where you can define the timeout rules for the Session. Common Session rules typically end a session after a period of 30 minutes of inactivity. Bringing a Session into Explore will allow you to get all sorts of valuable metrics such as Total Time in Sessions, Total Events in a Session, and more.
Note: The numbers and result does not need to be an exact match as the data changes over time. The query construction is what is most important. See images below.
*Click to enlarge*