diff --git a/kfet/statistic.py b/kfet/statistic.py
index 1db30d73..4ae17959 100644
--- a/kfet/statistic.py
+++ b/kfet/statistic.py
@@ -1,27 +1,29 @@
 # -*- coding: utf-8 -*-
 
 import ast
+from datetime import date, datetime, time, timedelta
 
 from dateutil.relativedelta import relativedelta
 
 from django.utils import timezone
 from django.db.models import Sum
 
-KFET_WAKES_UP_AT = 7
+KFET_WAKES_UP_AT = time(7, 0)
 
 
 def kfet_day(year, month, day, start_at=KFET_WAKES_UP_AT):
-    return timezone.datetime(year, month, day, hour=start_at)
+    """datetime wrapper with time offset."""
+    return datetime.combine(date(year, month, day), start_at)
 
 
 def to_kfet_day(dt, start_at=KFET_WAKES_UP_AT):
     kfet_dt = kfet_day(year=dt.year, month=dt.month, day=dt.day)
-    if dt.hour < start_at:
-        kfet_dt -= timezone.timedelta(days=1)
+    if dt.time() < start_at:
+        kfet_dt -= timedelta(days=1)
     return kfet_dt
 
 
-class StatScale(object):
+class Scale(object):
     name = None
     step = None
 
@@ -49,7 +51,7 @@ class StatScale(object):
 
     @staticmethod
     def by_name(name):
-        for cls in StatScale.__subclasses__():
+        for cls in Scale.__subclasses__():
             if cls.name == name:
                 return cls
         return None
@@ -80,9 +82,9 @@ class StatScale(object):
         return [begin.strftime(label_fmt) for begin, end in self]
 
 
-class DayStatScale(StatScale):
+class DayScale(Scale):
     name = 'day'
-    step = timezone.timedelta(days=1)
+    step = timedelta(days=1)
     label_fmt = '%A'
 
     @classmethod
@@ -90,19 +92,19 @@ class DayStatScale(StatScale):
         return to_kfet_day(dt)
 
 
-class WeekStatScale(StatScale):
+class WeekScale(Scale):
     name = 'week'
-    step = timezone.timedelta(days=7)
+    step = timedelta(days=7)
     label_fmt = 'Semaine %W'
 
     @classmethod
     def get_chunk_start(cls, dt):
         dt_kfet = to_kfet_day(dt)
-        offset = timezone.timedelta(days=dt_kfet.weekday())
+        offset = timedelta(days=dt_kfet.weekday())
         return dt_kfet - offset
 
 
-class MonthStatScale(StatScale):
+class MonthScale(Scale):
     name = 'month'
     step = relativedelta(months=1)
     label_fmt = '%B'
@@ -132,9 +134,9 @@ def stat_manifest(scales_def=None, scale_args=None, **url_params):
 
 def last_stats_manifest(scales_def=None, scale_args=None, **url_params):
     scales_def = [
-        ('Derniers mois', MonthStatScale, ),
-        ('Dernières semaines', WeekStatScale, ),
-        ('Derniers jours', DayStatScale, ),
+        ('Derniers mois', MonthScale, ),
+        ('Dernières semaines', WeekScale, ),
+        ('Derniers jours', DayScale, ),
     ]
     if scale_args is None:
         scale_args = {}
@@ -160,7 +162,7 @@ class ScaleMixin(object):
 
         scale_name = self.request.GET.get('scale', None)
 
-        cls = StatScale.by_name(scale_name)
+        cls = Scale.by_name(scale_name)
         if cls is None:
             scale = self.get_default_scale()
         else:
@@ -174,7 +176,7 @@ class ScaleMixin(object):
         return context
 
     def get_default_scale(self):
-        return DayStatScale(n_steps=7, last=True)
+        return DayScale(n_steps=7, last=True)
 
     def chunkify_qs(self, qs, scale, field=None):
         if field is None: