Vienna Philharmonic

Why not try the website and see?
https://www.wienerphilharmoniker.at/en/konzerte?v=30-06-2025&ia=f&iv=f&sm=f

That depends on the type of concert and the venue.

There is a series of subscription concerts, where subscribers get tickets assigned for several concerts during a season. These concerts are sold out from the onset, but you can get last minute tickets if subcribers waive their tickets. I guess there is a waiting list also. (By the way, you need to wait for years to get such a subscription, if ever. Mostly they are inherited from ancestors.)

Nevertheless, if you spot a concert you are interested in, try to book online at the venue as soon as possible. If there is a date given for the start of ticket sales, be pepared at that point in time, having already everything ready on the screen of your PC.

For certain big events, like the Salzburg Festival, getting tickets is really hard.

Look at the orchestra's concert schedule: https://www.wienerphilharmoniker.at/en/

It can be done with some planning. When I have gone, I have taken a standing ticket which allows you to hear and sort of see. In case it interests you, the Vienna Philharmonic musicians are also the musicians for the Vienna Opera. Just keep an eye on the website of the Vienna Philharmonic - tickets will go on sale for the fall season on Sept. 15. https://www.wienerphilharmoniker.at/en/konzerte?v=01-07-2025&ia=f&iv=f&sm=t

... tickets will go on sale for the fall season on Sept. 15.

This is the case for the first subscription concert, but not for others.

You need to click on "Buy Tickets" to get the accurate information when ticket sales will start for a specific concert.
E.g., for the concert on September 23, 2025 it will be revealed that sales will start on August 28, 2025 at 9am (local time).

To be prepared you should have created your user account in beforehand, got up in the night according your time zone, are already logged in, and try to get your tickets the very second the booking system will permit.