Your wedding date does not conflict with your birthday, because whenever you send an invitation, the wedding date on the invitation is September 30, that is, after your 25th birthday, so you can send it at any time. It is recommended to distribute it early.
As for marriage registration, it is best to call the local civil affairs department to find out the address and whether to go to work that day. If you go to work that day, it is recommended to queue up early, and the procedure will be faster.