Jumping into an RP usually means asking OOCly if you can join, most likely making a character-sheet, and then making an intro-post in the IC which is basically a cold-opening zeroth-session that gets your character up to speed with the story and everyone else up to speed with your character; at least up to speed enough to begin interacting with you.

Making an intro, but being so far removed from the group their characters aren't even aware of your character until 5 pages later is less than ideal. I've seen it done, it can work, but it's more work.