I introduced bottle to my baby once in the morning every day when she was one week old. Other than that she latch on demand. The earlier you introduced the bottle will help the transition once you return to work. I sent my baby to infant care when she was 4months old with no issue on the bottle feedings.
3 months. Using the smallest teat that has the slow/same flow as bfing. But it still depends on baby. My baby was on DL & bottle feeding since day 1. No issues.