If you go and ask most Germans (probably over 90-percent) about the voting process and Article 39 of the Basic Law (their Constitution).....most will give you a funny look and then go and have to look it up.
Article 39 is the basic rule on how voting will occur.
German law says that there is NOT a particular day that elections must occur (shocking for most Americans to grasp).
The 39th Article dictates that a national Bundestag election will occur between 46 and 48 months after the last election.
If there is a failure of the government (meaning that the coalition has failed), then the date shifts around. You could easily have one election on 1 March of one year, and twelve months later....face a failure of government, and have another election 1 June of the second year. Rarely do coalitions fail (as you might see in Italy frequently).
Several little unwritten rules fall into this play as well (not in Article 39)....for example....you rarely will ever have an election during school holiday periods or near Christmas.
You might want to also note that it's the Federal President (not the Chancellor) who orders the election date. The Chancellor might make the suggestion, but the President could go against that suggestion.
Always on a Sunday? Yes. This guarantees the bulk of society a chance to vote. Polling stations will open at 8AM and close by 6PM.
Locations of the polling stations? Generally, it's concreted down and you can ask people in your village or city about the location....it's the same place where it's been for forty-odd years.
Everyone who is registered....will get a letter about four to six weeks prior, and it'll make them aware of the date and the location. It'll also tell them to bring their national ID card. Giving some fake talk that you forgot your national ID? Well....it's kinda written down that when you leave the presence of your house and go anywhere.....you need that ID (on a bus, in a car, or hiking some trail). If the cops stop you....they will ask for it, and you have to present it. So, fake-chat on no ID....doesn't work.
If you did go and observe the 'flow' of traffic into a station....it's safe to say that most Germans will vote prior to noon. No one collects data much on this but I would take an educated guess that fifty to seventy percent of voters make the morning trip....instead of the afternoon trip.