Retrieves details about a replay. Use <code>DescribeReplay</code> to determine the progress of a running replay. A replay processes events to replay based on the time in the event, and replays them using 1 minute intervals. If you use <code>StartReplay</code> and specify an <code>EventStartTime</code> and an <code>EventEndTime</code> that covers a 20 minute time range, the events are replayed from the first minute of that 20 minute range first. Then the events from the second minute are replayed. You can use <code>DescribeReplay</code> to determine the progress of a replay. The value returned for <code>EventLastReplayedTime</code> indicates the time within the specified time range associated with the last event replayed.