Yes, intentional. That census was not carried out on a single date but throughout the month. Here’s what Ancestry say about it:
Because the official cutoff for the census was 12:01 a.m. on April 1, babies born later that day should not have been included. Residents of “hotels, tourist or trailer camps, missions, and cheap one-night lodging houses (flophouses)” were enumerated based on where they spent the night on 8 April 1940. Enumerators worked throughout the month and into May finishing the count.
But if you want to add a specific day you can edit the field as normal. You may have a specific date on the page you are transcribing.