Suggest you send Wilderness a 'thank you' letter for being kind enough to reply to you.Explain to them that it's an unusual courtesy on their part to even take the time in replying to your application. It will impress them that anyone bothers to point out how polite they have been in contacting you. It will also give you an opportunity to update your hours and let them know that, for them, you are instantly available because you'd so much like to work for a company that has such an excellent workforce ethos.
You could also send a copy of your short note translated into German, perhaps in your case, into English, just to remind them that you're at least bilingual. Native English speakers usually are monolingual, if not to say by educative process, monosyllabic.
The suggested answer to your question though, from a quick read through of the past umpteen years of posts, sounds like 500 hours?