Date constraint - Four weeks from todays date

1. What is the problem? Be very detailed.
I have added a constraint on date, so that entries more than 4 weeks from todays date can not go further in the form
I have added this in the xlsx form in the constraint column as:
int((today()-.) div 365.25) <= 28

I do not receive any errors, and the form uploads fine, but when I test it, any date over or under 4 weeks is allowed through to the next group.

2. What app or server are you using and on what device and operating system? Include version numbers.
ODK central

3. What you have you tried to fix the problem?
I have also tried to add the constraint as one month:
int((today()-.) div 365.25, ) <= 0.1

But this has the same results

4. What steps can we take to reproduce the problem?
I have attached my xlsx form

5. Anything else we should know or have? If you have a test form or screenshots or logs, attach below.ODK_test_forum.xlsx (16.3 KB)

Hi @bellbyrne
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As I said in Want to select date of last six month from the current date including current date - #2 by Grzesiek2010
You need to use decimal-date-time() function. In your case it would be like:
. > decimal-date-time(today())-28