@vianina
If it is of any help in your decision making on whether to scoot back or not, responses should be submitted by the 3rd May.
The law governing the census lists the below as offences, it makes no mention of late responses (unless they choose to class a late response as a failure to provide the information);
Article 21
Counter ordinations
Any of the following behaviours is an offence:
a) Failure to provide the information requested by INE, IP;
b) The provision of inaccurate, insufficient or susceptible to misleading information;
c) Opposition to the steps taken by the people involved in the work to collect the 2021 Census;
d) The refusal of access to the administrative information referred to in article 18.
It lists the applicable fine as being from €250 to €25,000 (which can be halved if the offence was due to negligence).