It takes approximately 36 hours for the sperm to fertilize the egg. That is about 1 day and 1/2. I would say wait at least 1 1/2 or 2 weeks before you take a pregnancy test so the results can come out accurate.
Generally, it takes about 10 to 14 days from the time of conception to accurately detect HCG in the urine. Conception may occur on a certain date however, it can take up to 3 to 4 days for actual implantation to occur. That means that you may have to wait a week to detect hcg at the proper levels.