From the composer.json its:
"require": {
"php": ">=5.3.2",
"symfony/framework-bundle": "~2.1",
"gedmo/doctrine-extensions": "~2.3.1"
}
This means that the current version of StofDoctrineExtensionsBundle will try and get doctrine-extensions between 2.3.1 and, not including, 2.4.
Composer will take care of finding the dependencies you need to make it run. I've included StofDoctrineExtensionsBundle in my projects to use Timestampable without any problems.
I recommend using the StofDoctrineExtensionsBundle.