diff --git a/src/main/kotlin/wanijo/wanijo2/domain/document.kt b/src/main/kotlin/wanijo/wanijo2/domain/document.kt
index 7b1f006..951f6eb 100644
--- a/src/main/kotlin/wanijo/wanijo2/domain/document.kt
+++ b/src/main/kotlin/wanijo/wanijo2/domain/document.kt
@@ -6,8 +6,7 @@ import org.springframework.data.jdbc.repository.query.Modifying
 import org.springframework.data.jdbc.repository.query.Query
 import org.springframework.data.relational.core.mapping.Table
 import org.springframework.data.repository.Repository
-import java.time.LocalDateTime
-import java.time.LocalDateTime.now
+import java.time.Instant
 import java.time.ZonedDateTime
 
 typealias DocumentId = Long
@@ -20,8 +19,8 @@ data class Document(
     val id: DocumentId = 0,
     val name: DocumentName,
     val description: DocumentDescription = "",
-    val updatedAt: LocalDateTime = now(),
-    val createdAt: LocalDateTime = now(),
+    val updatedAt: Instant = Instant.now(),
+    val createdAt: Instant = Instant.now(),
     val labelFields: Set<LabelField> = emptySet(),
     val dateFields: Set<DateField> = emptySet(),
 ) {
@@ -33,25 +32,25 @@ data class Document(
 
     fun withLabel(field: LabelField) =
         copy(
-            labelFields = labelFields + field,
-            updatedAt = now()
+            updatedAt = Instant.now(),
+            labelFields = labelFields + field
         )
 
     fun withDate(field: DateField) =
         copy(
-            dateFields = dateFields + field,
-            updatedAt = now()
+            updatedAt = Instant.now(),
+            dateFields = dateFields + field
         )
 
     fun withoutLabel(fieldId: FieldId) =
         copy(
-            updatedAt = now(),
+            updatedAt = Instant.now(),
             labelFields = labelFields.filter { it.id != fieldId }.toSet()
         )
 
     fun withoutDate(fieldId: FieldId) =
         copy(
-            updatedAt = now(),
+            updatedAt = Instant.now(),
             dateFields = dateFields.filter { it.id != fieldId }.toSet()
         )
 }
@@ -61,7 +60,7 @@ data class DocumentBrief(
     @Id
     val id: DocumentId,
     val name: DocumentName,
-    val updatedAt: ZonedDateTime
+    val updatedAt: Instant
 )
 
 interface DocumentDao : Repository<Document, DocumentId> {
diff --git a/src/main/kotlin/wanijo/wanijo2/domain/event/AddDateFieldCommand.kt b/src/main/kotlin/wanijo/wanijo2/domain/event/AddDateFieldCommand.kt
index 87bddcf..4fe8f09 100644
--- a/src/main/kotlin/wanijo/wanijo2/domain/event/AddDateFieldCommand.kt
+++ b/src/main/kotlin/wanijo/wanijo2/domain/event/AddDateFieldCommand.kt
@@ -17,11 +17,4 @@ data class AddDateFieldCommand(
     @NotEmpty
     val dateValue: LocalDateTime,
     val order: Int = 0,
-) {
-    fun toField() =
-        DateField(
-            name = dateName,
-            value = dateValue,
-            order = order
-        )
-}
+)
diff --git a/src/main/kotlin/wanijo/wanijo2/domain/fields.kt b/src/main/kotlin/wanijo/wanijo2/domain/fields.kt
index e8ddab6..daf49a7 100644
--- a/src/main/kotlin/wanijo/wanijo2/domain/fields.kt
+++ b/src/main/kotlin/wanijo/wanijo2/domain/fields.kt
@@ -2,8 +2,8 @@ package wanijo.wanijo2.domain
 
 import org.springframework.data.annotation.Id
 import org.springframework.data.relational.core.mapping.Table
+import java.time.Instant
 import java.time.LocalDateTime
-import java.time.LocalDateTime.now
 
 typealias FieldId = Long
 
@@ -14,8 +14,8 @@ data class LabelField(
     val order: Int = 0,
     val name: String,
     val value: String = "",
-    val updatedAt: LocalDateTime = now(),
-    val createdAt: LocalDateTime = now(),
+    val updatedAt: Instant = Instant.now(),
+    val createdAt: Instant = Instant.now(),
 )
 
 @Table("T_DATE_FIELD")
@@ -25,6 +25,6 @@ data class DateField(
     val order: Int = 0,
     val name: String,
     val value: LocalDateTime,
-    val updatedAt: LocalDateTime = now(),
-    val createdAt: LocalDateTime = now(),
+    val updatedAt: Instant = Instant.now(),
+    val createdAt: Instant = Instant.now()
 )
diff --git a/src/main/kotlin/wanijo/wanijo2/domain/handler/AddDateFieldHandler.kt b/src/main/kotlin/wanijo/wanijo2/domain/handler/AddDateFieldHandler.kt
index 50779ad..93552b9 100644
--- a/src/main/kotlin/wanijo/wanijo2/domain/handler/AddDateFieldHandler.kt
+++ b/src/main/kotlin/wanijo/wanijo2/domain/handler/AddDateFieldHandler.kt
@@ -3,7 +3,6 @@ package wanijo.wanijo2.domain.handler
 import org.springframework.stereotype.Service
 import wanijo.wanijo2.domain.DateField
 import wanijo.wanijo2.domain.DocumentDao
-import wanijo.wanijo2.domain.LabelField
 import wanijo.wanijo2.domain.event.AddDateFieldCommand
 import wanijo.wanijo2.http.DocumentNotFound
 
@@ -15,7 +14,13 @@ class AddDateFieldHandler(
     fun exec(command: AddDateFieldCommand) {
         val doc = documentDao.findById(command.documentId) ?: throw DocumentNotFound()
         documentDao.save(
-            doc.withDate(command.toField())
+            doc.withDate(
+                DateField(
+                    name = command.dateName,
+                    value = command.dateValue,
+                    order = command.order
+                )
+            )
         )
     }
 
diff --git a/src/main/kotlin/wanijo/wanijo2/domain/tag.kt b/src/main/kotlin/wanijo/wanijo2/domain/tag.kt
index 9a6cd0a..a6862d9 100644
--- a/src/main/kotlin/wanijo/wanijo2/domain/tag.kt
+++ b/src/main/kotlin/wanijo/wanijo2/domain/tag.kt
@@ -6,9 +6,9 @@ import org.springframework.data.jdbc.repository.query.Modifying
 import org.springframework.data.jdbc.repository.query.Query
 import org.springframework.data.relational.core.mapping.Table
 import org.springframework.data.repository.Repository
+import java.time.Instant
 import java.time.LocalDateTime
 import java.time.LocalDateTime.now
-import java.time.ZonedDateTime
 
 typealias TagId = Long
 typealias TagName = String
@@ -18,7 +18,7 @@ data class Tag(
     @Id
     val id: TagId = 0,
     val name: TagName,
-    val createdAt: LocalDateTime = now()
+    val createdAt: Instant = Instant.now()
 )
 
 typealias DocumentTaggingId = Long
@@ -29,7 +29,7 @@ data class DocumentTagging(
     val id: DocumentTaggingId = 0,
     val tagId: AggregateReference<Tag, TagId>,
     val documentId: AggregateReference<Document, DocumentId>,
-    val createdAt: LocalDateTime = now()
+    val createdAt: Instant = Instant.now()
 ) {
     companion object {
         fun between(doc: Document, tagId: TagId) =