ITR filing is done online. Even though the due date was Sunday, the ITR filing can be done online on a Sunday. The fact that CA office is closed on Sunday is not a convincing justification to allow the belated return to be considered as filed within due date. Moreover, the individual assessee should not have waited for last moment to file the ITR.
As per section 119(2)(b) of the Income Tax Act, the Board may, if it considers it desirable or expedient so to do for avoiding genuine hardship in any case or class of cases, by general or special order, authorise any income-tax authority, not being a Commissioner (Appeals) to admit an application or claim for any exemption, deduction, refund or any other relief under this Act after the expiry of the period specified by or under this Act for making such application or claim and deal with the same on merits in accordance with law;
In my humble opinion this situation is not 'genuine hardship' and hence the department's stand is correct.