diff --git a/CHANGES.txt b/CHANGES.txt
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,5 +1,8 @@
 Changelog for Extra
 
+1.6
+    #23, delete subtractTime
+    Require QuickCheck-2.10
 1.5.3
     Add readMaybe, readEither
 1.5.2
diff --git a/extra.cabal b/extra.cabal
--- a/extra.cabal
+++ b/extra.cabal
@@ -1,7 +1,7 @@
 cabal-version:      >= 1.18
 build-type:         Simple
 name:               extra
-version:            1.5.3
+version:            1.6
 license:            BSD3
 license-file:       LICENSE
 category:           Development
@@ -69,8 +69,7 @@
         filepath,
         extra,
         clock >= 0.7,
-        time,
-        QuickCheck >= 2.9
+        QuickCheck >= 2.10
     if !os(windows)
         build-depends: unix
     hs-source-dirs: test
diff --git a/src/Extra.hs b/src/Extra.hs
--- a/src/Extra.hs
+++ b/src/Extra.hs
@@ -53,7 +53,7 @@
     system_, systemOutput, systemOutput_,
     -- * System.Time.Extra
     -- | Extra functions available in @"System.Time.Extra"@.
-    Seconds, sleep, timeout, subtractTime, showDuration, offsetTime, offsetTimeIncrease, duration,
+    Seconds, sleep, timeout, showDuration, offsetTime, offsetTimeIncrease, duration,
     -- * Text.Read.Extra
     -- | Extra functions available in @"Text.Read.Extra"@.
     readEither, readMaybe,
diff --git a/src/System/IO/Extra.hs b/src/System/IO/Extra.hs
--- a/src/System/IO/Extra.hs
+++ b/src/System/IO/Extra.hs
@@ -103,7 +103,7 @@
 
 -- | Write a binary file.
 --
--- > \s -> withTempFile $ \file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file
+-- > \(ASCIIString s) -> withTempFile $ \file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file
 writeFileBinary :: FilePath -> String -> IO ()
 writeFileBinary file x = withBinaryFile file WriteMode $ \h -> hPutStr h x
 
diff --git a/src/System/Time/Extra.hs b/src/System/Time/Extra.hs
--- a/src/System/Time/Extra.hs
+++ b/src/System/Time/Extra.hs
@@ -8,13 +8,11 @@
 module System.Time.Extra(
     Seconds,
     sleep, timeout,
-    subtractTime,
     showDuration,
     offsetTime, offsetTimeIncrease, duration
     ) where
 
 import Control.Concurrent
-import Data.Time.Clock
 import System.Clock
 import Numeric.Extra
 import Control.Monad.Extra
@@ -70,16 +68,6 @@
                    (bracket (forkIOWithUnmask $ \unmask -> unmask $ sleep n >> throwTo pid ex)
                             killThread
                             (\_ -> fmap Just f))
-
-
--- Once we remove subtractTime we can remove the dependency on the time package entire.
-{-# DEPRECATED subtractTime "Function is being retired - use diffUTCTime directly." #-}
-
--- | Calculate the difference between two times in seconds.
---   Usually the first time will be the end of an event, and the
---   second time will be the beginning.
-subtractTime :: UTCTime -> UTCTime -> Seconds
-subtractTime end start = fromRational $ toRational $ end `diffUTCTime` start
 
 
 -- | Show a number of seconds, typically a duration, in a suitable manner with
diff --git a/test/TestGen.hs b/test/TestGen.hs
--- a/test/TestGen.hs
+++ b/test/TestGen.hs
@@ -224,7 +224,7 @@
     testGen "isWindows == (os == \"mingw32\")" $ isWindows == (os == "mingw32")
     testGen "\\(filter isHexDigit -> s) -> fmap (== s) $ withTempFile $ \\file -> do writeFile file s; readFile' file" $ \(filter isHexDigit -> s) -> fmap (== s) $ withTempFile $ \file -> do writeFile file s; readFile' file
     testGen "\\s -> withTempFile $ \\file -> do writeFileUTF8 file s; fmap (== s) $ readFileUTF8' file" $ \s -> withTempFile $ \file -> do writeFileUTF8 file s; fmap (== s) $ readFileUTF8' file
-    testGen "\\s -> withTempFile $ \\file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file" $ \s -> withTempFile $ \file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file
+    testGen "\\(ASCIIString s) -> withTempFile $ \\file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file" $ \(ASCIIString s) -> withTempFile $ \file -> do writeFileBinary file s; fmap (== s) $ readFileBinary' file
     testGen "captureOutput (print 1) == return (\"1\\n\",())" $ captureOutput (print 1) == return ("1\n",())
     testGen "withTempFile doesFileExist == return True" $ withTempFile doesFileExist == return True
     testGen "(doesFileExist =<< withTempFile return) == return False" $ (doesFileExist =<< withTempFile return) == return False
diff --git a/test/TestUtil.hs b/test/TestUtil.hs
--- a/test/TestUtil.hs
+++ b/test/TestUtil.hs
@@ -1,6 +1,13 @@
 {-# LANGUAGE ScopedTypeVariables, CPP, FlexibleInstances #-}
 
-module TestUtil(runTests, testGen, testRaw, erroneous, erroneousIO, (====), module X) where
+module TestUtil
+    (runTests
+    ,testGen, testRaw
+    ,erroneous, erroneousIO
+    ,(====)
+    ,ASCIIString(..)
+    ,module X
+    ) where
 
 import Test.QuickCheck
 import Test.QuickCheck.Test
@@ -10,8 +17,6 @@
 import Data.Version.Extra
 import Data.IORef
 import System.IO.Unsafe
-import Data.Time.Clock
-import Data.Time.Calendar
 import Text.Show.Functions()
 
 import Extra as X
@@ -70,9 +75,6 @@
     n <- readIORef testCount
     putStrLn $ "Success (" ++ show n ++ " tests)"
 
-instance Testable () where
-    property = property . (`seq` True)
-
 instance Testable a => Testable (IO a) where
     property = property . unsafePerformIO
 
@@ -95,12 +97,3 @@
 
 instance Eq SomeException where
     a == b = show a == show b
-
-instance Arbitrary UTCTime where
-    arbitrary = liftM2 UTCTime arbitrary arbitrary
-
-instance Arbitrary Day where
-    arbitrary = fmap ModifiedJulianDay arbitrary
-
-instance Arbitrary DiffTime where
-    arbitrary = realToFrac <$> choose (0 :: Double, 86401)