All right.
I have to, before or after the 13th of October?
whenever you want just dont use the old client anymore for anything but exporting your keys.
Daft question maybe: does the wallet need to fully sync?
yes and no. if there have been transactions between your last indexed/scanned block and 13th october, you need to sync.
but if you are absolutely sure there were no transactions then you can skip syncing.
so its better to sync just to be sure