  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework import ISO_8601
  from rest_framework.compat import (
      get_remote_field, unicode_repr, unicode_to_repr, value_from_object
  )
  from rest_framework.exceptions import ErrorDetail, ValidationError
  from rest_framework.settings import api_settings
  from rest_framework.utils import html, humanize_datetime, representation
  
 
</s> remove from django.utils.timezone import pytz, utc
 </s> add from django.utils.timezone import utc </s> remove from rest_framework import serializers
 </s> add from rest_framework import compat, serializers </s> remove     field = serializers.DateTimeField(default_timezone=pytz.timezone('America/New_York'))
 </s> add     class MockTimezone:
        @staticmethod
        def localize(value, is_dst):
            raise compat.InvalidTimeError()

        def __str__(self):
            return 'America/New_York'

    field = serializers.DateTimeField(default_timezone=MockTimezone()) </s> remove             except Exception:
 </s> add             except InvalidTimeError:
    InvalidTimeError, get_remote_field, unicode_repr, unicode_to_repr,
    value_from_object
  from django.utils.translation import ugettext_lazy as _
  
  from rest_framework import ISO_8601
  from rest_framework.compat import (
    InvalidTimeError, get_remote_field, unicode_repr, unicode_to_repr,
    value_from_object
  )
  from rest_framework.exceptions import ErrorDetail, ValidationError
  from rest_framework.settings import api_settings
  from rest_framework.utils import html, humanize_datetime, representation
  
keep keep keep keep replace keep keep keep keep keep
 Added pytz exception in compat module.
Mock pytz.timezone localize in tests.
Ref: #4986 
rest_framework/fields.py