It's pretty quick to plant bare-root seedlings using a spade or "dibble". About 45 years ago another Boy Scout and I planted approximately 1,000 pine seedlings on a tree farm in a single day using a variant of the method shown in [1]. Once we got a rhythm going we planted around 3 trees per minute.
[1] https://www.youtube.com/watch?v=jhqa3yeLxhk