The 5-day rule is permissive ("the administrative law judge may decline to accept the evidence"), and often is not enforced. But if you show up at the hearing with new evidence, you are taking a risk. Your claim-winning medical source statement may not be admitted into the record. There are exceptions to the rule, so if you have late evidence, have your story ready for the judge.
Sometimes a claims fall off the DSI/electronic-file track for some reason, and the disability claim file is an old-style paper file. For these cases, the "normal" rules apply, and there is not 5-day limit for new evidence. Regardless, it is a best practice to submit evidence into the record as soon as possible.