I'm sure the timelines are slightly different, but maybe by weeks, not by months or years.
There is no need to even PLACE an indictment in advance. Sometimes (usually) that happens AFTER the arrest. With more complex inditements, prepare over a period od weeks. File on day one and arrest on day one. Filing is a leak vector. There are crooked courts.
Federal grand jury witnesses are not bound to any secrecy. That’s why politically-charged grand jury actions are almost always ‘leaked’. Witnesses want to talk about political questioning.