Sri K.N. Rao has demonstrated the use of the double transit phenomenon of Jupiter and Saturn in the timing of the birth of children, the rise and fall in career, and marriages through various articles and books that he's published since the mid 1980's. If you are not familiar with this method it will become clear in the following example chart that is based on an article that Rao published in the Jan-Mar 2003 issue of the Journal of Astrology.
This is the Vedic astrology chart of a woman who was married in April 2002. At that time she was in her Saturn-Mer-Saturn dasha. Notice how Saturn rules the 7th house of marriage and Mercury is located in the 7th house. Also, Saturn and Mercury form a parivartana yoga or exchange of signs - Mercury is in Saturn's sign of Aquarius, while Saturn is in Mercury's sign of Virgo. This forms a close connection between these two planets, which becomes activated during this dasha. This sets the stage for the potential for marriage during this time period.
In addition, at the time of marriage, in April 2002, Saturn and Jupiter were both aspecting the 7th house of Aquarius. Any house that is aspected by both Jupiter and Saturn represents an area in the person's life that can undergo great progress. This is called the double transit phenomenon. Saturn was transiting through Taurus and aspected Aquarius with its 10th house aspect. While Jupiter was transiting through Gemini, and aspected Aquarius with its 9th house aspect. Both the dashas and transits indicated the same event of marriage during this time period.
Transits April 2002