diff --git a/lib/Providers/Personal/CollectionResource.php b/lib/Providers/Personal/CollectionResource.php
index 57ead50..160f89b 100644
--- a/lib/Providers/Personal/CollectionResource.php
+++ b/lib/Providers/Personal/CollectionResource.php
@@ -9,6 +9,7 @@ declare(strict_types=1);
 
 namespace KTXM\ProviderLocalPeople\Providers\Personal;
 
+use KTXF\Utile\Timestamp;
 use KTXF\People\Collection\CollectionMutableAbstract;
 use KTXF\Resource\Identifier\CollectionIdentifier;
 
@@ -73,8 +74,8 @@ class CollectionResource extends CollectionMutableAbstract {
 			'rank' => $properties->getRank(),
 			'visibility' => $properties->getVisibility(),
 			'color' => $properties->getColor(),
-			'createdOn' => $this->data[self::PROPERTY_CREATED] ?? null,
-			'modifiedOn' => $this->data[self::PROPERTY_MODIFIED] ?? null,
+			'createdOn' => Timestamp::normalize($this->data[self::PROPERTY_CREATED] ?? null),
+			'modifiedOn' => Timestamp::normalize($this->data[self::PROPERTY_MODIFIED] ?? null),
 			'signature' => $this->data[self::PROPERTY_SIGNATURE] ?? null,
 			'enabled' => $this->collectionEnabled,
 		], static fn($value) => $value !== null);
diff --git a/lib/Providers/Personal/EntityResource.php b/lib/Providers/Personal/EntityResource.php
index 26f943f..81b3a7f 100644
--- a/lib/Providers/Personal/EntityResource.php
+++ b/lib/Providers/Personal/EntityResource.php
@@ -47,8 +47,8 @@ class EntityResource extends EntityMutableAbstract {
 			'uid' => $this->userId,
 			'cid' => $this->collection(),
 			'eid' => $this->identifier(),
-			'createdOn' => $this->data[self::PROPERTY_CREATED] ?? date('c'),
-			'modifiedOn' => date('c'),
+			'createdOn' => Timestamp::normalize($this->data[self::PROPERTY_CREATED] ?? null),
+			'modifiedOn' => Timestamp::normalize($this->data[self::PROPERTY_MODIFIED] ?? null),
 		], static fn($value) => $value !== null);
 
 		$document = array_merge($document, $this->getProperties()->toStore());
diff --git a/lib/Store/Personal/Store.php b/lib/Store/Personal/Store.php
index 76a6ce6..0c20fcc 100644
--- a/lib/Store/Personal/Store.php
+++ b/lib/Store/Personal/Store.php
@@ -9,6 +9,7 @@ declare(strict_types=1);
 
 namespace KTXM\ProviderLocalPeople\Store\Personal;
 
+use KTXF\Utile\Timestamp;
 use KTXC\Db\DataStore;
 use KTXF\Resource\Filter\Filter;
 use KTXF\Resource\Filter\FilterComparisonOperator;
@@ -252,7 +253,7 @@ class Store {
 		$data['uid'] = $userId;
 		$data['cid'] = UUID::v4();
 		$data['signature'] = isset($data['signature']) && is_numeric($data['signature']) ? (int)$data['signature'] : 0;
-		$data['createdOn'] = date('c');
+		$data['createdOn'] = Timestamp::now();
 		$data['modifiedOn'] = $data['createdOn'];
 		// create entry
 		$result = $this->_store->selectCollection($this->_CollectionTable)->insertOne($data);
@@ -280,7 +281,7 @@ class Store {
 		if ($cid === null) {
 			throw new \InvalidArgumentException('Collection identifier is required for modification');
 		}
-		$data['modifiedOn'] = date('c');
+		$data['modifiedOn'] = Timestamp::now();
 		unset($data['_id'], $data['tid'], $data['uid'], $data['cid']);
 		// modify entry
 		$this->_store->selectCollection($this->_CollectionTable)->updateOne(
@@ -370,8 +371,8 @@ class Store {
 				/** @var \KTXF\Resource\Range\IRangeDate $rangeDate */
 				$rangeDate = $range;
 				$query['data.startsOn'] = [
-					'\$gte' => $rangeDate->getStart()->format('c'),
-					'\$lte' => $rangeDate->getEnd()->format('c')
+					'\$gte' => Timestamp::toIso8601($rangeDate->getStart()) ?? throw new \InvalidArgumentException('Invalid epoch millisecond range boundary'),
+					'\$lte' => Timestamp::toIso8601($rangeDate->getEnd()) ?? throw new \InvalidArgumentException('Invalid epoch millisecond range boundary')
 				];
 			}
 		}
@@ -486,7 +487,7 @@ class Store {
 		$data['uid'] = $userId;
 		$data['cid'] = $collectionId;
 		$data['eid'] = UUID::v4();
-		$data['createdOn'] = date('c');
+		$data['createdOn'] = Timestamp::now();
 		$data['createdBy'] = $userId;
 		$data['modifiedOn'] = $data['createdOn'];
 		$data['modifiedBy'] = $data['createdBy'];
@@ -518,7 +519,7 @@ class Store {
 	public function entityModify(string $tenantId, string $userId, string $collectionId, string $identifier, EntityResource $entity): EntityResource {
 		// convert entity to store format
 		$data = $entity->toStore();
-		$data['modifiedOn'] = date('c');
+		$data['modifiedOn'] = Timestamp::now();
 		$data['modifiedBy'] = $userId;
 		// Remove identifiers from update data (they shouldn't change)
 		unset($data['_id'], $data['tid'], $data['uid'], $data['cid'], $data['eid']);
@@ -632,7 +633,7 @@ class Store {
 			'eid' => $eid,
 			'operation' => $operation,
 			'signature' => $signature,
-			'mutatedOn' => time(),
+			'mutatedOn' => Timestamp::now(),
 		]);
 		
 		// update signature as normalized numeric value