Here is a summary of a nursery production schedule for fruit trees:
• Late fall: Cut/dig rootstock liners.
• Early spring: Plant liners.
• Late summer: Bud rootstock liner.
• Early spring: Cut off top of rootstock liner above bud.
• Late fall: Dig finished trees.
• Early spring: Sell/ship finished trees.
See this article titled Nursery Production of Finished Apple Trees for more detailed information.
Answer provided by Robert Crassweller, Penn State University.