Multiple customs of when to start putting on tefilin exist, one of such being to start the day a boy turns 13. If that day occurs on Shabbes, are there any customs to begin putting on Tefillin on the Friday before? This is something I have heard people mentioning.
Nitei Gavriel - Bar Mitzvah discusses this. He mentions that there are those that will wait until Sunday, those that will start of Friday, and those that will start Friday without a Bracha.