The advice I remember is that one should take DAT before application cycle opens, so that if they don't obtain their desired score, they'll have a second chance in summer because there's a wait period between taking DAT. I took my DAT late May last cycle, but the thing is, I also see a lot of folks submitting their application and then taking DAT (and doing well), and it still seems to work out fine so your personal preferences come into play here, too.