Hi. I've potted several seedlings in early and mid-April, so very recently. They all had some root structure, so they weren't just cut cuttings. They are all taking very well so far. Some are branching out more aggressively than others, but all are top some degree.

My question is, when should I start thinking about pruning to promote ramification? Should I wait a year for that?

You are looking at 3 to 5 years, it depends on species and growth. There is not much to do apart from watering for that time.

Ramicication comes after creating a good nebari, nice trunk size and tapering and chosing main branches.

Once you are happy with those features pruning for ramification is the priority.