if you have made a tax return before you will get the paperwork eventually. in the mean time play with your cantons tax software. it does most of the work for you!

end of march is the CH standard submission date. a first delay of 3-6 months is easy/automatic to obtain and most cantons have a website that you can request this. another 3-6 delay after that usually requires an explanation why you need the additional time. after that you are pretty much on a penalty of some sort + interest of the debt you owe.