What updates to the index are included in a snapshot?

If I have a snapshot like this:

    duration_in_millis: 963
    end_time: "2015-09-04T04:00:02.141Z"
    end_time_in_millis: 1441339202141
    failures: []
    shards: {total: 10, failed: 0, successful: 10}
    snapshot: "snapshot_20150903"
    start_time: "2015-09-04T04:00:01.178Z"
    start_time_in_millis: 1441339201178
    state: "SUCCESS"

I'm wondering what updates to the index will be included in the snapshot:

all updates before start_time_in_millis?
all updates before end_time_in_millis?