The Electoral Commission publishes a timetable of legal deadlines for each of the May elections. They’re in PDF here, but it’s useful for us to keep the details of some of them - like the date of notice of persons nominated, notice of polls, in one place.
In case it’s useful to anyone else:
It doesn’t include everything that’s in the Electoral Commission’s guidance, so if you are so minded, please complete the Google Sheets here. (Please do request access if required).