Yeah, you can enter the code on the 23rd, but for me it won't be enough at least, mail won't even arrive on Firday here because it's a holiday.

AFAIK, RDM and SAM are listed under 4.0 content, so I honestly don't know if you can access them without the expansion. Same with levels 60-70 on any jobs might be tied to the expansion, so I assume if I suddenly default to lvl 60, even the gear I wear will cause some errors. Regardless, better safe than sorry.