diff --git a/src/yunohost/app.py b/src/yunohost/app.py
index 0664a24b2..79af7faf2 100644
--- a/src/yunohost/app.py
+++ b/src/yunohost/app.py
@@ -37,7 +37,6 @@ import pwd
 import grp
 from collections import OrderedDict
 import datetime
-import pytz
 
 from moulinette import msignals, m18n, msettings
 from moulinette.core import MoulinetteError
@@ -83,9 +82,8 @@ def app_listlists():
     appslist_list = _read_appslist_list()
 
     for app in appslist_list:
-        last_update = datetime.datetime.utcfromtimestamp(
+        appslist_list[app]["lastUpdate"] = datetime.datetime.utcfromtimestamp(
             appslist_list[app].get("lastUpdate"))
-        appslist_list[app]["lastUpdate"] = last_update.replace(tzinfo=pytz.utc)
 
     return appslist_list
 
@@ -1762,7 +1760,7 @@ def _get_app_status(app_id, format_date=False):
             if not v:
                 status[f] = '-'
             else:
-                status[f] = datetime.utcfromtimestamp(v).replace(tzinfo=pytz.utc)
+                status[f] = datetime.utcfromtimestamp(v)
     return status
 
 
diff --git a/src/yunohost/backup.py b/src/yunohost/backup.py
index 492687eaf..528b2e24f 100644
--- a/src/yunohost/backup.py
+++ b/src/yunohost/backup.py
@@ -33,7 +33,6 @@ import shutil
 import subprocess
 import csv
 import tempfile
-import pytz
 from datetime import datetime
 from glob import glob
 from collections import OrderedDict
@@ -301,7 +300,7 @@ class BackupManager():
             (string) A backup name created from current date 'YYMMDD-HHMMSS'
         """
         # FIXME: case where this name already exist
-        return time.strftime('%Y%m%d-%H%M%S')
+        return time.strftime('%Y%m%d-%H%M%S', time.gmtime())
 
     def _init_work_dir(self):
         """Initialize preparation directory
@@ -2268,8 +2267,7 @@ def backup_info(name, with_details=False, human_readable=False):
 
     result = {
         'path': archive_file,
-        'created_at': datetime.utcfromtimestamp(info['created_at'])
-                        .replace(tzinfo=pytz.utc),
+        'created_at': datetime.utcfromtimestamp(info['created_at']),
         'description': info['description'],
         'size': size,
     }
diff --git a/src/yunohost/log.py b/src/yunohost/log.py
index c75300d3d..af19090c8 100644
--- a/src/yunohost/log.py
+++ b/src/yunohost/log.py
@@ -101,7 +101,7 @@ def log_list(category=[], limit=None):
             except ValueError:
                 pass
             else:
-                entry["started_at"] = log_datetime.replace(tzinfo=pytz.utc)
+                entry["started_at"] = log_datetime
 
             result[category].append(entry)
 
@@ -321,8 +321,7 @@ class OperationLogger(object):
         """
 
         if self.started_at is None:
-            self.started_at = datetime.utcnow()
-            self.started_at = self.started_at.replace(tzinfo=pytz.utc)
+            self.started_at = datetime.now(tz=pytz.utc)
             self.flush()
             self._register_log()
 
@@ -414,8 +413,7 @@ class OperationLogger(object):
             return
         if error is not None and not isinstance(error, basestring):
             error = str(error)
-        self.ended_at = datetime.utcnow()
-        self.ended_at = self.ended_at.replace(tzinfo=pytz.utc)
+        self.ended_at = datetime.now(tz=pytz.utc)
         self._error = error
         self._success = error is None
         if self.logger is not None:
diff --git a/src/yunohost/monitor.py b/src/yunohost/monitor.py
index cad467ed5..fc10a4fbc 100644
--- a/src/yunohost/monitor.py
+++ b/src/yunohost/monitor.py
@@ -283,7 +283,7 @@ def monitor_system(units=None, human_readable=False):
         elif u == 'process':
             result[u] = json.loads(glances.getProcessCount())
         elif u == 'uptime':
-            result[u] = (str(datetime.utcnow() - datetime.utcfromtimestamp(psutil.boot_time())).split('.')[0])
+            result[u] = (str(datetime.now() - datetime.fromtimestamp(psutil.boot_time())).split('.')[0])
         elif u == 'infos':
             result[u] = json.loads(glances.getSystem())
         else:
diff --git a/src/yunohost/service.py b/src/yunohost/service.py
index 73383cb44..fd75d0235 100644
--- a/src/yunohost/service.py
+++ b/src/yunohost/service.py
@@ -31,7 +31,6 @@ import subprocess
 import errno
 import shutil
 import hashlib
-import pytz
 
 from difflib import unified_diff
 from datetime import datetime
@@ -276,7 +275,6 @@ def service_status(names=[]):
             }
             if "ActiveEnterTimestamp" in status:
                 result[name]['active_at'] = datetime.utcfromtimestamp(status["ActiveEnterTimestamp"] / 1000000)
-                result[name]['active_at'] = result[name]['active_at'].replace(tzinfo=pytz.utc)
             else:
                 result[name]['active_at'] = "unknown"
 
@@ -926,7 +924,7 @@ def _process_regen_conf(system_conf, new_conf=None, save=True):
     """
     if save:
         backup_path = os.path.join(BACKUP_CONF_DIR, '{0}-{1}'.format(
-            system_conf.lstrip('/'), time.strftime("%Y%m%d.%H%M%S")))
+            system_conf.lstrip('/'), datetime.utcnow().strftime("%Y%m%d.%H%M%S")))
         backup_dir = os.path.dirname(backup_path)
 
         if not os.path.isdir(backup_dir):