we used both from the beginning, and mixed it up between day and night.
DS was always going to only have a few months in the hammock bcause he was so long, so I didn't want him to get used only to it, but it was great because I could move it from one room to the next.
He was still a little jaundice when we came home from hospital so I could move him in front of whichever window had the most sunlight coming through it.