Sounds like maybe you were ovulating. As long as your cm is fertile there is a possibility of conceiving. Which if yours was clear not creamy then it would be classed as fertile.

As for the "window of opportunity", that's a bit more difficult. Sperm can live up to 3-5 days in the uterus but the egg survives a lot less (can remember - maybe 24hrs?).

If you are unsure of your cycles, i think it is recommended to test no sooner than 14 days after dtd to get an accurate result on your hpt.

for you!