They did, didn't they?
I'm not sure, but didn't the first show take 3 days - 1 for the guys, 1 for the girls, and a 3rd for the results show? If so, presuming (like scd) the day of the actual show is spent at the studios getting make up, dress rehearsals etc., the couples could only have had 3 days to learn and practice their routines, which isn't that long.