It isn't really a big deal. The few extra months you get in the Jan class gives you more time to study for boards and more vacation at the end. Obviously the january class puts you a year behind given you are in the same class as the august. I was in the january class and would have rather done the august to not delay myself but doesn't really matter much. Either way you have plenty of time to study for boards and do everything you need to.
Do you think there are issues when it comes to residency or anything later since a January join date would be off-cycle... like people will have a harder time remembering you since there is a year gap later?