We missed the window to book advanced reservation online. What are the chances if we wait in line for a same day visit (or even a tour)? We can manage to wait in line for ~1 hour but maybe not much more than that. Are there better time? early morning or late in the evening?
I don't know whether waiting in line at the Reichstag itself does you any good. Page 763 of Rick's Germany book suggests:
If you're in Berlin without a reservation, try dropping by the tiny visitors center on the Tiergarten side of Scheidemannstrasse, across from Platz der Republik. A screen in its window shows which hourly slots, over the next three days, still have tickets available (open daily April-Oct 8:00-20:00, Nov-March 8:00-18:00; go between 8:00-10:00 to avoid lines; you must book no less than 2 hours and no more than 2 days out; when booking, the whole party must be present and ID is required).