If you're still looking for information, as far as I know, plastic recorders don't need a breaking in period. I think that wood needs to adjust to the moisture and warmth of playing, but plastic is much more forgiving that way. Hope you're having fun with your new tenor. =) Is this your first tenor recorder?
I do tend to notice that my plastic tenor and bass Yamahas sound a bit better now than they did a couple years ago, though that may only be because of practice, embouchure/breathing development, and aural skills on my behalf.
I can't answer the original question as to break-in, though it's possible that right at first your embouchure, etc. will need a few sessions to adjust to the new instrument. Hope it goes well. A GOOD plastic tenor can be one of the best recorder investments you ever make.
A plastic instrument does not need any break in period. It is one of the benefits of plasstic. . . it is what it is, and stays that way. IF it sounds better as you play, it is not the instrument, but the result of your learning how to play it better. You will adjust to it, and you will improve!