Hi!
Both my pregnancies were discovered 10 days after conception or 3 days before my period (but I didn't know it because my period was irregular, it's the sonogram that gave the conception date). SO if you're really really impatient you can try but if the test is not positive remember that it doesn't mean your not pregnant, it might just mean that the concentration of hormone is not yet high enough. Do the test in the morning.
It's probably wiser to wait a couple of days, and it depends a bit on your budget!!!
Good luck