Aduh mama, memang tough situation ni sebab baby purely BF dan sudden separation lagi kan... Honestly a few of my mum friends did this and most babies took 2-3 weeks to settle, tapi malam adalah fasa paling challenging sebab baby memang cari comfort dari ibu dia, bukan saja lapar je. Yang penting atok nenek kena patient and consistent dengan bottle feeding, jangan give up kalau first few nights baby cry, at malam memang dia akan demand susu and cry for you, it's normal, but slowly dia akan adapt lah bila realise mummy tak datang. I suggest maybe do a trial run dulu sebelum you fully start work, so at least baby ada few weeks to adjust to the new routine and faces, plus you boleh pulang weekend awal-awal to help settle dia, tiap anak lain timing dia, so talk to your paediatrician jugak about the transition plan sebab concern kamu tu valid and dokter boleh guide berapa lama memang realistic and what to watch for.