A system according to certain aspects improves the process of performing snapshot replication operations (e.g., maintaining a mirror copy of primary data at a secondary location by generating snapshots of the primary data). The system can collect and maintain cumulative block-level changes to the primary data after each sub-interval of a plurality of sub-intervals between the snapshots. When a snapshot is generated, any changes to the primary data not reflected in the cumulative block-level changes are identified based on the snapshot and transmitted to the secondary location along with the cumulative block-level changes. By the time the snapshot is generated, some or all of the changes to the primary data associated with the given snapshot have already been included in the cumulative block-level changes, thereby reducing the time and computing resources spent to identify and collect the changes for transmission to the secondary location.