OK !

So, i finaly use:

dd |/| mm |/| yy yy |;| hh |:| mm |:| ss |;| XX => 22bytes
dmy;h:m:s;X => 11 bytes !

11 x (48 x 30) => 15840 bytes => 16k EEPROM !!

I think i will buy a "24AA16"

Thank you