Submission dates for tax returns - in my gemeinde (local community) these can be extended to pretty much any month of the year I like, as long as I request this in advance (which can also be done via a website). This spreads the administrative load for the tax department in your community, since the returns don't all arrive at once.

In the case of a tax return arriving without a submission date, then the standard procedure (like for any such situation) would simply be to call the person who sent the letter and ask them. If there is no contact person listed, then simply phone or visit the tax department at your local community office and ask. I'm sure they don't bite and would readily give you this information.

Some other people also seem to have been asking "How long before I get my money back". Well, I suspect that the answer to this will vary widely according to the usual regional shenanigans in Switzerland, but in my case, for canton Zurich, my refunds have usually taken 3 years to come through and I was told this is normal. Personally I find a such a level of service a complete joke, but I'm not going to hop on my soapbox here... I'm still waiting for my refund from 2002.

If you can speak German and need the money in a hurry, you can sometimes call your cantonal tax department, and after a bit of digging they may be able to tell you which particular paper mountain it is located in, and how much longer it might take. It's important to mention that you were paying tax at source, because these tax returns are handled (at least in Zurich) by a separate department.