|By statute, the census starts on April 1, 2020. Come hell, high water, or war, that date has never been missed in over 200 years, and it will not be missed this year.|
The Census Bureau has started an on-line early response program for some reason, but it's flawed because the final questionnaire has not been decided and they've included the disputed citizenship question. It's also optional - you're not required to comply. Assuming the SCOTUS decision sending the question back down to a lower court is not reversed before April 1, 2020, any responses to that question will have to be ignored.
The citizenship question has been raised in previous censuses, but only in targeted areas around the country. It was never asked nationally and was elimainated after 1950 (I think) because it was found to cause undercounts - which it will do in 2020 if it's reinstated.
Personally, I would have ignored those emails to go online. The official counting doesn't start until next April, and I have no idea where or if I'll be by then...