diff --git a/stix2/v20/common.py b/stix2/v20/common.py
index ecc93b1..19c43d8 100644
--- a/stix2/v20/common.py
+++ b/stix2/v20/common.py
@@ -15,16 +15,16 @@ from ..utils import NOW, _get_dict
 
 
 def _should_set_millisecond(cr, marking_type):
-        if marking_type == TLPMarking:
+    if marking_type == TLPMarking:
+        return True
+    if type(cr) == str:
+        if '.' in cr:
             return True
-        if type(cr) == str: 
-            if '.' in cr:
-                return True
-            else: 
-                return False
-        if cr.precision == 'millisecond':
-            return True
-        return False
+        else:
+            return False
+    if cr.precision == 'millisecond':
+        return True
+    return False
 
 
 class ExternalReference(_STIXBase):
diff --git a/stix2/v21/common.py b/stix2/v21/common.py
index 4b13def..ca97597 100644
--- a/stix2/v21/common.py
+++ b/stix2/v21/common.py
@@ -1,7 +1,6 @@
 """STIX 2.1 Common Data Types and Properties."""
 
 from collections import OrderedDict
-import copy
 
 from ..base import _STIXBase
 from ..custom import _custom_marking_builder
@@ -14,6 +13,7 @@ from ..properties import (
 )
 from ..utils import NOW, _get_dict
 
+
 class ExternalReference(_STIXBase):
     # TODO: Add link
     """For more detailed information on this object's properties, see