diff --git a/custom_metadata.php b/custom_metadata.php
index 6aa50aa..afe827f 100644
--- a/custom_metadata.php
+++ b/custom_metadata.php
@@ -1063,14 +1063,24 @@ function _sanitize_field_value( $field_slug, $field, $object_type, $object_id, $
 
 		$sanitize_callback = $this->get_sanitize_callback( $field, $object_type );
 
+		if ( $sanitize_callback )
+			return call_user_func( $sanitize_callback, $field_slug, $field, $object_type, $object_id, $value );
+
 		// convert date to unix timestamp
 		if ( in_array( $field->field_type, array( 'datepicker', 'datetimepicker', 'timepicker' ) ) ) {
-			$value = strtotime( $value );
+			
+			// if $value is an array, we need to sanitize every value in the array
+			if( is_array( $value ) ) {
+				$result = array();
+				foreach ( $value as $val ) {
+					$result[] = strtotime( $val );
+				}
+				$value = $result;
+			} else {
+				$value = strtotime( $value );
+			}
 		}
 
-		if ( $sanitize_callback )
-			return call_user_func( $sanitize_callback, $field_slug, $field, $object_type, $object_id, $value );
-
 		return $value;
 	}