I've never tried for standing room at the Staatsoper; however, the following information was posted to an international opera forum by a very knowledgable local in 2003:

Yes, standing room tickets are sold 75 minutes before the start
of the performance, for Euro 3.50 (Stehparterre, just between the
most expensive boxes, best view) or 2.00 (gallery for the best
acoustics, or balcony if nothing else is left).

About 45 minutes before the performance, you can get into the
audience, mark your place in the standing room area (places are
not numbered) with a handkerchief or shawl and then you are
free to go out for a quick supper and to be back on your place
15 minutes before the performance. You get "Vilar titles" even
at each standing place, in German and English for all operas,
even those sung in German, but not for ballets.

Doors open 3 hours before the performance. Usually, it is sufficient
to be there about 90 minutes before the performance.

For very few top performances (premieres), they issus "numbers"
at 6 a.m. . people queue up for the numbers early in the morning,
then go home (or to work) and have to at the doors 3 hours before
the performance where they enter accordning to their numbers.


Good luck in your quest to get there on time (and BTW Keenleyside should sing (and act) a great Don).