Note that the CAT train from the airport to Vienna only goes twice an hour - 06 and 36 (07 and 37 going back). Time your walk to the platform so that you only arrive five minutes before it goes - the platforms are cold and windy and there are few places to sit. If you've just missed one when you arrive in the arrivals hall, you are better staying up there and having a coffee for 15 minutes. On the other hand, don't dawdle in arrivals if one is about to go! Give yourself 5-6 mins (assuming no heavy luggage) to get to the train from arrivals.