Honestly hindi ako sure sa exact expiration timeline ng Mat 2, pero from what I've heard sa friends ko na nag-file, ang concern usually ay kung complete ang documents mo when you submit, hindi ganit kalaki ang issue kung slightly delayed ang birth cert copy basta na-file mo na agad. I'd suggest contact your HR or payroll directly to clarify kung may specific deadline sila for submitting the birth certificate, kasi bawat company may slightly different process, tapos peace of mind mo na rin agad!