Talking to Anne I realized that opening hours are different in Vienna and it might be a good idea to spell it out.
For people who want to go to any of the Museums. Check their opening hours first!
Many museums are closed on Mondays. So if you want to go plan another day or at least check. Sundays are generally good days to visit Museums.
I would also assume that all close at 18.00 and early/late evening is also no option.
Sunday is basically a day where every shop is closed. Even some Restaurants and Pubs are closing. You should not worry about the restaurants/pubs - enough will be open and you will find something to eat. No doubt.
Shops are often closing at 6pm with exceptions on big shopping streets like Mariahilferstrasse where shops may stay open until 7 or later (especially on Thursdays or Fridays, very unlikely on Saturdays).
Supermarkets the same...... no food shopping on Sundays. Water, juices etc. for the room (to avoid mini bar prices) you need to buy before Sunday and before 6pm on Saturdays.