Hi! Based sa karanasan ko, usually pwede ka nang mag-file ng SSS sickness benefit during your leave pa lang or right after, pero best talaga na i-check mo directly sa SSS mismo or sa HR mo kasi bawat employer may slight differences sa process nila. I learned this the hard way when I filed late and nag-hassle ang lahat haha, mas madali kung prepared ka na with all the requirements like medical certificate at company certification. Good luck, mama!