How do you analyze the data captured by an Extended Events session once it has been running for a period of time?

You can open the event file target directly in SQL Server Management Studio, which provides a graphical interface for viewing and filtering the captured events, or query the file programmatically using the sys.fn_xe_file_target_read_file function to extract the data into a table format for more detailed custom analysis.

SELECT event_data.value('(event/@timestamp)[1]', 'datetime2') AS EventTime,
       event_data.value('(event/data[@name="duration"]/value)[1]', 'bigint') AS Duration
FROM sys.fn_xe_file_target_read_file('LongQueries*.xel', NULL, NULL, NULL)
CROSS APPLY (SELECT CAST(event_data AS XML) AS event_data) AS ed;