If the cycle is regular, then you can buy tests already for 1-3 days of delay. If not, it is better to wait at least another 2-3 days or take the test several times with an interval of three days.
In cases where a woman does everything to get pregnant, she can try to find out the result even a couple of days before the expected menstruation. To do this, she will need an inkjet or electronic test, since other options are not sensitive enough for such a short period.
On the 7th day of delay, in the absence of specific diseases and proper use, any tests will reliably show whether a woman is pregnant or not.
The answer to this question is in the instructions, since each product is individual. As a rule, the waiting time does not exceed 20 minutes. Strips take longer, but inkjet, electronic and tablet wands are faster.
Another criterion is the gestational age. The smaller it is, the longer the result appears. In a test with poor sensitivity, daytime and evening urine may generally give a false negative response.
There is a separate category of test-strip cases that are misleading. The product may not detect pregnancy after the specified period of time. However, after an hour or even a day, a second strip will appear on it. It does not necessarily indicate a successful conception. It is better to play it safe and go through the procedure again or contact a gynecologist.