Communication networks and associated methods are disclosed that provide charging for long duration sessions. A charging data system of the communication network receives interim accounting request messages from a network element that is serving a session. The charging data system identifies interim timestamps for the interim accounting request messages, and stores the interim timestamps. After a time period during the long duration session, the charging data system generates a partial CDR. The charging data system then inserts duration information for the long duration session in the partial CDR based on the stored interim timestamps, and transmits the partial CDR to a correlation system. The correlation system may then calculate a total duration for the session based on the duration information in the partial CDR. Even if a start/stop timestamp is not available, the correlation system may estimate the total duration of the session based on the interim timestamps.