Changing vibrate length of default email app on galaxy s2
There are two methods you can use to adjust the vibration duration:

System Configuration

Tap your device &quot;home&quot; button;
Tap your device &quot;menu&quot; button;
Tap &quot;Settings&quot;;
Tap &quot;Sound&quot;;
Use &quot;Vibration Intensity&quot; to adjust the duration.

This may not be available for all devices/Android versions

Custom Application
There are a few applications available from Google Play Store that you can use to adjust vibration timers.
Vibration Notifier by j4velin allows you to set a vibrate interval and additionally alows you to specify the duration of each vibration:

Let your device vibrate every X min. when you missed a call / received an eMail