I've been thinking: a twin is born at 11:59 p.m. on February 29th [in a leap year] and the sibling is born like 23 minutes later on March 1st. One would have a birthday only every 4 years.
or
how odd it must be if one twin is born December 31st like at 11:57 p.m. and then the sibling is born January 1st ->the next year<- at like 01:09 a.m.
-> born a year apart but twins.

I've got to find more things to keep my mind from wandering so much.
and I'll apologize now to any twins out there that may have been offended by this.
none was intended.