According to the manual, the rookie draft only includes players that made their first appearance the most recent major league season. As I read this in the Real Time leagues, that means the rookie draft list is already set - it includes all first year players that did not get enough playing time to make the monthly drafts in the previous season or weren't drafted during them.

So as far as I understood, no rookies making their first appearance the begining of this season would be in the rookie draft no matter how much playing time they got before the rookie draft took place. As soon as they get enough playing time, they should be put in the free agent pool.

In other words, say Rookie Pitcher A gets his first ML appearance in April, and by the 18th he has enough innings to qualify to be drafted. He would not be put into the rookie draft, as this is for last years rookies. He would be put into the free agent draft as the rules state that once a rookie has enough playing time he is eligible for the next scheduled free agent draft.

So no matter when the rookie draft is held, the current list is set, and no new rookies can be added.