Premature ejaculation is the occurrence of the male orgasm before the woman is ready. There is no time limit. For some couples, the male orgasm will be considered premature if it happens in less than 30 minutes after the initiation of lovemaking. If the man comes in 30 seconds, it might be O.K. if the women comes in 30 seconds or less. This would also be a very economical use of their time. Busy people might strive for this type of efficiency.
As with all couple problems, communication is the key. Once the couple have decided that they want to delay the male orgasm, they can do it.
What doesn't work, and should never be tried, is for the man to think of something else (like baseball or pizza or whatever). This may delay the orgasm slightly, but wouldn't be much fun for either partner. Frequent use of this technique will lead to impotence.
For the man to delay his ejaculation he must anticipate the sensation of an impending orgasm. This is when the man knows he will have an orgasm very soon. This can be anticipated by all men. At that point the stimulation must stop immediately. The woman needs to know when this point has been reached and cooperate. After a minute or two the man's erection will soften slightly and stimulation can be resumed. This can be done over and over again in a session of love making. This has the obvious benefit for the woman of giving her plenty of time to achieve her own satisfaction. The man gets two big benefits. First, he participates in his partners greater satisfaction. Second, his orgasm, when it occurs, will be more intense than usual.
In general, women have their most intense orgasm after one to four prior ones. Men have the most intense sensation after the longest period of lovemaking and the maximum number of approaches to orgasm that stop just in time.