Some men and women have such unrealistic expectations. The pressure to perform can trigger the ejaculation they wish to delay. Pressure is also created by the common belief that sex is over when the man ejaculates.
Most people agree that a man who usually climaxes within seconds of insertion has a problem.
It's completely subjective. Instead of measuring by the clock, consider the reasons behind a speedy climax. Rapid ejaculation sometimes reflects psychological issues, such as fear of sex or women, self-consciousness or guilt about desires. Secretive, rushed masturbation trains many men for this kind of quick release. Most rapid ejaculators attempt to distract themselves during sex, thinking this will reduce the perceived stimulation and delay the orgasm.