Heroku apps run on a normal unix system, and you have all the zoneinfo files there. I'm also fairly sure they're up-to-date.
As far as unix goes, you should be able to set your TZ env var with something like:
$ heroku config:set TZ=Europe/Berlin
You can see the valid zoneinfo names with:
$ heroku run find /usr/share/zoneinfo/posix
Generally speaking, though, you'll want to run your application on an UTC environment, and handle timezones internally, possibly handling local time on a user-per-user basis.
I suspect this may not entirely answer your question. You might want to expand on what exactly you're trying to achieve and how you're trying to achieve it, and also how you are observing the "one hour less than local" effect.
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