diff --git a/log.cabal b/log.cabal
--- a/log.cabal
+++ b/log.cabal
@@ -1,5 +1,5 @@
 name:                log
-version:             0.3.1
+version:             0.4
 synopsis:            Structured logging solution with multiple backends
 
 description:         A library that provides a way to record structured log messages with multiple backends.
@@ -28,8 +28,8 @@
                        Log.Backend.PostgreSQL,
                        Log.Backend.StandardOutput,
                        Log.Class,
-                       Log.Class.Instances,
                        Log.Data,
+                       Log.Internal.Logger,
                        Log.Logger,
                        Log.Monad
 
@@ -43,7 +43,7 @@
                        hpqtypes >=1.4,
                        lifted-base,
                        monad-control >=0.3,
-                       monad-time,
+                       monad-time >= 0.2,
                        mtl,
                        old-locale,
                        split,
diff --git a/src/Log/Backend/StandardOutput.hs b/src/Log/Backend/StandardOutput.hs
--- a/src/Log/Backend/StandardOutput.hs
+++ b/src/Log/Backend/StandardOutput.hs
@@ -8,4 +8,4 @@
 
 -- | Create logger that prints messages to standard output.
 stdoutLogger :: IO Logger
-stdoutLogger = mkLogger "stdout" $ T.putStrLn . showLogMessage
+stdoutLogger = mkLogger "stdout" $ T.putStrLn . showLogMessage Nothing
diff --git a/src/Log/Class.hs b/src/Log/Class.hs
--- a/src/Log/Class.hs
+++ b/src/Log/Class.hs
@@ -1,4 +1,6 @@
-{-# LANGUAGE OverlappingInstances #-}
+{-# OPTIONS_GHC -fno-warn-deprecated-flags #-}
+{-# LANGUAGE FlexibleContexts, FlexibleInstances, OverlappingInstances
+  , RankNTypes, UndecidableInstances #-}
 module Log.Class (
     UTCTime
   , MonadTime(..)
@@ -12,7 +14,8 @@
   ) where
 
 import Control.Monad.Time
-import Control.Monad.Time.Instances ()
+import Control.Monad.Trans
+import Control.Monad.Trans.Control
 import Data.Aeson
 import Data.Aeson.Types
 import Data.Time
@@ -25,6 +28,20 @@
   logMessage  :: UTCTime -> LogLevel -> T.Text -> Value -> m ()
   localData   :: [Pair] -> m a -> m a
   localDomain :: T.Text -> m a -> m a
+
+-- | Generic, overlapping instance.
+instance (
+    MonadLog m
+  , Monad (t m)
+  , MonadTransControl t
+  ) => MonadLog (t m) where
+    logMessage time level message = lift . logMessage time level message
+    localData data_ m = controlT $ \run -> localData data_ (run m)
+    localDomain domain m = controlT $ \run -> localDomain domain (run m)
+
+controlT :: (MonadTransControl t, Monad (t m), Monad m)
+         => (Run t -> m (StT t a)) -> t m a
+controlT f = liftWith f >>= restoreT . return
 
 ----------------------------------------
 
diff --git a/src/Log/Class/Instances.hs b/src/Log/Class/Instances.hs
deleted file mode 100644
--- a/src/Log/Class/Instances.hs
+++ /dev/null
@@ -1,23 +0,0 @@
-{-# OPTIONS_GHC -fno-warn-orphans #-}
-{-# LANGUAGE FlexibleContexts, FlexibleInstances, OverlappingInstances
-  , RankNTypes, UndecidableInstances #-}
-module Log.Class.Instances () where
-
-import Control.Monad.Trans
-import Control.Monad.Trans.Control
-
-import Log.Class
-
--- | Generic, overlapping instance.
-instance (
-    MonadLog m
-  , Monad (t m)
-  , MonadTransControl t
-  ) => MonadLog (t m) where
-    logMessage time level message = lift . logMessage time level message
-    localData data_ m = controlT $ \run -> localData data_ (run m)
-    localDomain domain m = controlT $ \run -> localDomain domain (run m)
-
-controlT :: (MonadTransControl t, Monad (t m), Monad m)
-         => (Run t -> m (StT t a)) -> t m a
-controlT f = liftWith f >>= restoreT . return
diff --git a/src/Log/Data.hs b/src/Log/Data.hs
--- a/src/Log/Data.hs
+++ b/src/Log/Data.hs
@@ -53,10 +53,12 @@
 , lmData      :: !Value
 } deriving (Eq, Show)
 
-showLogMessage :: LogMessage -> T.Text
-showLogMessage LogMessage{..} = T.concat $ [
+showLogMessage :: Maybe UTCTime -> LogMessage -> T.Text
+showLogMessage mInsertionTime LogMessage{..} = T.concat $ [
     T.pack $ formatTime defaultTimeLocale "%Y-%m-%d %H:%M:%S" lmTime
-  , " "
+  , case mInsertionTime of
+      Nothing -> " "
+      Just it -> T.pack $ formatTime defaultTimeLocale " (%H:%M:%S) " it
   , T.toUpper $ showLogLevel lmLevel
   , " "
   , T.intercalate "/" $ lmComponent : lmDomain
diff --git a/src/Log/Internal/Logger.hs b/src/Log/Internal/Logger.hs
new file mode 100644
--- /dev/null
+++ b/src/Log/Internal/Logger.hs
@@ -0,0 +1,39 @@
+{-# LANGUAGE RecordWildCards #-}
+module Log.Internal.Logger (
+    Logger(..)
+  , execLogger
+  , waitForLogger
+  ) where
+
+import Control.Concurrent.STM
+import Data.IORef
+
+import Log.Data
+
+-- | Data type representing logger.
+data Logger = Logger {
+  loggerWriteMessage :: !(LogMessage -> IO ())
+, loggerWaitForWrite :: !(STM ())
+, loggerFinalizers   :: ![IORef ()]
+}
+
+-- | Execute logger to serialize a 'LogMessage'.
+execLogger :: Logger -> LogMessage -> IO ()
+execLogger Logger{..} = loggerWriteMessage
+
+-- | Wait until logs stored in an internal queue are serialized.
+waitForLogger :: Logger -> IO ()
+waitForLogger Logger{..} = atomically loggerWaitForWrite
+
+-- | Composition of 'Logger' objects.
+instance Monoid Logger where
+  mempty = Logger (const $ return ()) (return ()) []
+  l1 `mappend` l2 = Logger {
+    loggerWriteMessage = \msg -> do
+      loggerWriteMessage l1 msg
+      loggerWriteMessage l2 msg
+  , loggerWaitForWrite = do
+      loggerWaitForWrite l1
+      loggerWaitForWrite l2
+  , loggerFinalizers = loggerFinalizers l1 ++ loggerFinalizers l2
+  }
diff --git a/src/Log/Logger.hs b/src/Log/Logger.hs
--- a/src/Log/Logger.hs
+++ b/src/Log/Logger.hs
@@ -18,7 +18,20 @@
 import qualified Data.Text.IO as T
 
 import Log.Data
+import Log.Internal.Logger
 
+-- | Make 'Logger' that consumes one queued message at a time.
+mkLogger :: T.Text -> (LogMessage -> IO ()) -> IO Logger
+mkLogger = mkLoggerImpl
+  newTQueueIO isEmptyTQueue readTQueue writeTQueue $ return ()
+
+-- | Make 'Logger' that consumes all queued messages once per second.
+mkBulkLogger :: T.Text -> ([LogMessage] -> IO ()) -> IO Logger
+mkBulkLogger = mkLoggerImpl
+  newSQueueIO isEmptySQueue readSQueue writeSQueue $ threadDelay 1000000
+
+----------------------------------------
+
 -- | Simple STM based queue.
 newtype SQueue a = SQueue (TVar [a])
 
@@ -41,48 +54,6 @@
 -- | Write a value to an 'SQueue'.
 writeSQueue :: SQueue a -> a -> STM ()
 writeSQueue (SQueue queue) a = modifyTVar queue (a :)
-
-----------------------------------------
-
--- | Opaque data type representing logger.
-data Logger = Logger {
-  loggerWriteMessage :: !(LogMessage -> IO ())
-, loggerWaitForWrite :: !(STM ())
-, loggerFinalizers   :: ![IORef ()]
-}
-
--- | Execute logger to serialize a 'LogMessage'.
-execLogger :: Logger -> LogMessage -> IO ()
-execLogger Logger{..} = loggerWriteMessage
-
--- | Wait until logs stored in an internal queue are serialized.
-waitForLogger :: Logger -> IO ()
-waitForLogger Logger{..} = atomically loggerWaitForWrite
-
--- | Composition of 'Logger' objects.
-instance Monoid Logger where
-  mempty = Logger (const $ return ()) (return ()) []
-  l1 `mappend` l2 = Logger {
-    loggerWriteMessage = \msg -> do
-      loggerWriteMessage l1 msg
-      loggerWriteMessage l2 msg
-  , loggerWaitForWrite = do
-      loggerWaitForWrite l1
-      loggerWaitForWrite l2
-  , loggerFinalizers = loggerFinalizers l1 ++ loggerFinalizers l2
-  }
-
-----------------------------------------
-
--- | Make 'Logger' that consumes one queued message at a time.
-mkLogger :: T.Text -> (LogMessage -> IO ()) -> IO Logger
-mkLogger = mkLoggerImpl
-  newTQueueIO isEmptyTQueue readTQueue writeTQueue $ return ()
-
--- | Make 'Logger' that consumes all queued messages once per second.
-mkBulkLogger :: T.Text -> ([LogMessage] -> IO ()) -> IO Logger
-mkBulkLogger = mkLoggerImpl
-  newSQueueIO isEmptySQueue readSQueue writeSQueue $ threadDelay 1000000
 
 ----------------------------------------