it all depends on your ovulation, if you were keeping track of it. If not, two weeks after conception, or 4 or 5 days after your missed period... if you get a negative and don't get your period after another two weeks, retest.
Sometimes, a cycle can be as long as 40-days. Time of day shouldn't matter, I think. The hormone they test for goes up in your system in detectable amounts day-by-day; not sure if hour-to-hour would have significant differences.
When I was worried about getting pregnant, I stocked up on super basic early detection tests so that I wouldn't have to worry about some $10-20 test every time I was unsure. I got a pack of 5 on Amazon for $5 â€” super handy. Good luck!