Below is the query to generate a list for a defined timeframe of user connections and the duration of the connection.
// Session duration by date
// Lists users by session duration in the last 24 hours.
// The "State" provides information on the connection stage of an actitivity.
// The delta between "Connected" and "Completed" provides the connection time for a specific connection.
WVDConnections
| where TimeGenerated > ago(30d)
| where State == "Connected"
| project CorrelationId , UserName, ConnectionType , StartTime=TimeGenerated, Date=format_datetime(TimeGenerated, 'MM-dd-yyyy')
| join (WVDConnections
| where State == "Completed"
| project EndTime=TimeGenerated, CorrelationId)
on CorrelationId
| project Date, Duration = EndTime - StartTime, ConnectionType, UserName
| sort by Date desc