Double ended question. How do you know you've conceived without a pregnancy test? Only other way to tell you've gotten pregnant is by missing several months. That's the old fashioned way. So is injecting a rabbit then killing it to see if it got pregnant. Yup they used to do that too. Horrid for rabbits.
the best time is 2 to 3 weeks. you can get early detection tests but these only work some of the time as being so close to conception you can get false negatives. i say give it a few weeks and then try a test and then another 4 or 5 days later