Most HPTs recommend waiting until the first day of your missed period. The second part of the cycle is mosr regular than the first in women - in other words, when women vary from a 21 day cycle to a 32 day cycles, it is usually the bit before ovulation that is varying; the bit afterwards is a fairly constant 14 days. So testing on the first day of your missed period usually gives you a reliable 14 DPO time lapse from conception, if it occurred.

Once more, any experts feel free to jump in...