For how many days this should be done?

It's good for all of us actually. You can keep the baby in sunlight for some time as long as you want ...I used to keep my daughter near the window and sometimes in the balcony too...

Early morning sunshine is good for new born babies. You may try from day 1. Just do not keep them exposed to much. I used to keep my son near window for morning sun light. So that he isn't exposed much yet he get sun light