diff --git a/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DataRecord.java b/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DataRecord.java
index 934ec3d09..54001c449 100644
--- a/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DataRecord.java
+++ b/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DataRecord.java
@@ -26,9 +26,30 @@
 public class DataRecord {
     private final String idempotencyKey;
     private final String status;
+
+    /**
+     * This field is controlling how long the result of the idempotent
+     * event is cached. It is stored in _seconds since epoch_.
+     *
+     * DynamoDB's TTL mechanism is used to remove the record once the
+     * expiry has been reached, and subsequent execution of the request
+     * will be permitted. The user must configure this on their table.
+     */
     private final long expiryTimestamp;
     private final String responseData;
     private final String payloadHash;
+
+    /**
+     * The in-progress field is set to the remaining lambda execution time
+     * when the record is created.
+     * This field is stored in _milliseconds since epoch_.
+     *
+     * This ensures that:
+     *
+     * 1/ other concurrently executing requests are blocked from starting
+     * 2/ if a lambda times out, subsequent requests will be allowed again, despite
+     *     the fact that the idempotency record is already in the table
+     */
     private final OptionalLong inProgressExpiryTimestamp;
 
     public DataRecord(String idempotencyKey, Status status, long expiryTimestamp, String responseData, String payloadHash) {
diff --git a/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStore.java b/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStore.java
index 47ddf4c5c..6b5d0fcb2 100644
--- a/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStore.java
+++ b/powertools-idempotency/src/main/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStore.java
@@ -126,6 +126,19 @@ public DataRecord getRecord(String idempotencyKey) throws IdempotencyItemNotFoun
         return itemToRecord(response.item());
     }
 
+    /**
+     * Store's the given idempotency record in the DDB store. If there
+     * is an existing record that has expired - either due to the
+     * cache expiry or due to the in_progress_expiry - the record
+     * will be overwritten and the idempotent operation can continue.
+     *
+     * <b>Note: This method writes only expiry and status information - not
+     * the results of the operation itself.</b>
+     *
+     * @param record DataRecord instance to store
+     * @param now
+     * @throws IdempotencyItemAlreadyExistsException
+     */
     @Override
     public void putRecord(DataRecord record, Instant now) throws IdempotencyItemAlreadyExistsException {
         Map<String, AttributeValue> item = new HashMap<>(getKey(record.getIdempotencyKey()));
@@ -152,6 +165,7 @@ public void putRecord(DataRecord record, Instant now) throws IdempotencyItemAlre
 
             Map<String, AttributeValue> expressionAttributeValues = Stream.of(
                     new AbstractMap.SimpleEntry<>(":now", AttributeValue.builder().n(String.valueOf(now.getEpochSecond())).build()),
+                    new AbstractMap.SimpleEntry<>(":now_milliseconds", AttributeValue.builder().n(String.valueOf(now.toEpochMilli())).build()),
                     new AbstractMap.SimpleEntry<>(":inprogress", AttributeValue.builder().s(INPROGRESS.toString()).build())
             ).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
 
@@ -160,7 +174,7 @@ public void putRecord(DataRecord record, Instant now) throws IdempotencyItemAlre
                     PutItemRequest.builder()
                             .tableName(tableName)
                             .item(item)
-                            .conditionExpression("attribute_not_exists(#id) OR #expiry < :now OR (attribute_exists(#in_progress_expiry) AND #in_progress_expiry < :now AND #status = :inprogress)")
+                            .conditionExpression("attribute_not_exists(#id) OR #expiry < :now OR (attribute_exists(#in_progress_expiry) AND #in_progress_expiry < :now_milliseconds AND #status = :inprogress)")
                             .expressionAttributeNames(expressionAttributeNames)
                             .expressionAttributeValues(expressionAttributeValues)
                             .build()
diff --git a/powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStoreTest.java b/powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStoreTest.java
index 86e35cd33..768da2eaa 100644
--- a/powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStoreTest.java
+++ b/powertools-idempotency/src/test/java/software/amazon/lambda/powertools/idempotency/persistence/DynamoDBPersistenceStoreTest.java
@@ -95,7 +95,7 @@ public void putRecord_shouldCreateRecordInDynamoDB_IfLambdaWasInProgressAndTimed
         Map<String, AttributeValue> item = new HashMap<>(key);
         Instant now = Instant.now();
         long expiry = now.plus(30, ChronoUnit.SECONDS).getEpochSecond();
-        long progressExpiry = now.minus(30, ChronoUnit.SECONDS).getEpochSecond();
+        long progressExpiry = now.minus(30, ChronoUnit.SECONDS).toEpochMilli();
         item.put("expiration", AttributeValue.builder().n(String.valueOf(expiry)).build());
         item.put("status", AttributeValue.builder().s(DataRecord.Status.INPROGRESS.toString()).build());
         item.put("data", AttributeValue.builder().s("Fake Data").build());
@@ -152,14 +152,14 @@ public void putRecord_shouldThrowIdempotencyItemAlreadyExistsException_IfRecordA
     }
 
     @Test
-    public void putRecord_shouldThrowIdempotencyItemAlreadyExistsException_IfRecordAlreadyExistAndProgressNotExpiredAfterLambdaTimedOut() {
+    public void putRecord_shouldBlockUpdate_IfRecordAlreadyExistAndProgressNotExpiredAfterLambdaTimedOut() {
         key = Collections.singletonMap("id", AttributeValue.builder().s("key").build());
 
         // GIVEN: Insert a fake item with same id
         Map<String, AttributeValue> item = new HashMap<>(key);
         Instant now = Instant.now();
         long expiry = now.plus(30, ChronoUnit.SECONDS).getEpochSecond(); // not expired
-        long progressExpiry = now.plus(30, ChronoUnit.SECONDS).getEpochSecond(); // not expired
+        long progressExpiry = now.plus(30, ChronoUnit.SECONDS).toEpochMilli(); // not expired
         item.put("expiration", AttributeValue.builder().n(String.valueOf(expiry)).build());
         item.put("status", AttributeValue.builder().s(DataRecord.Status.INPROGRESS.toString()).build());
         item.put("data", AttributeValue.builder().s("Fake Data").build());
@@ -172,10 +172,10 @@ public void putRecord_shouldThrowIdempotencyItemAlreadyExistsException_IfRecordA
                 new DataRecord("key",
                         DataRecord.Status.INPROGRESS,
                         expiry2,
-                        null,
+                        "Fake Data 2",
                         null
-                ), now)
-        ).isInstanceOf(IdempotencyItemAlreadyExistsException.class);
+                ), now))
+                .isInstanceOf(IdempotencyItemAlreadyExistsException.class);
 
         // THEN: item was not updated, retrieve the initial one
         Map<String, AttributeValue> itemInDb = client.getItem(GetItemRequest.builder().tableName(TABLE_NAME).key(key).build()).item();