It is a controversy always when people ask about Twins especially when they try to reconcile their Bazi to reality.
I mean its normal that twins does have slightly different characters and outcome in life. Thus modern practitioners tries hard to find an answer to accommodate the difference in the outcome. One of the popular theory that took wave is the notion that the younger twins should be given an earlier Chinese hour.
For example, if the twin was born at 10am while the second twin was born say some minutes later (assuming natural birth), then the first twin will have born in the hour of Si 巳 while the younger twin will be assigned the earlier hour of Chen 辰.
For those not familiar with Chinese hour system, Si or Snake hour is between 9am to 10:59am. Before Si hour is the Chen hour or Dragon hour which is between 7am to 8:59am.
However, this new theory contradicts traditional rules of Bazi which says your birth hour is the hour of birth. Thus if you are born in the Si hour, thus you will be having a Si in your hour pillar. What is the rational then of pushing the younger twin one Chinese hour earlier.?
If the case were to be like this, http://ktla.com/2016/11/11/twins-born-as-daylight-saving-time-ends-cause-rare-age-twist/, I can rational the difference in Chinese hour of birth but to force the second child to have a different hour is perhaps something that needs to be reviewed.