Hello,
What to do to prevent the user from any more editing (add new data, modify the pre-entered data) at specific date? may to show an alarte message to the user such like (The editing for this form is no more available).
regards.
The details on controlling form access from Central are detailed here: https://docs.getodk.org/central-projects/#managing-form-access
A method within the XLSForm will depend on the device date & time, which means that someone could hack the process by manually changing their phone's date & time.