There are four columns in the table nas_transaction_summary dealing with time. All of these are times from the local nas probe, not the originating probe. Here is a short description of each:
This is the timestamp recorded for the first alarm in this transaction. This column could have null values
This records the creation time of the transaction and should carry the same value as in the nimts
This records the closure time of the transaction, null if this transaction has not been closed.
This records the timestamp of the latest actions(new alarms,update,close,acknowledged,assigned) in this transaction. For a closed transaction the value of time equals to the value of closed, so for a new transaction this should be the same as the value of created.