Riddle cuddle!!! 03/2012

They are part of triplets, or quadruplets....etc. 

Ya....any day could be same like sunday...monday .....................saturday.Its day not date

Just because they were not born at the same time on same date of the same year..

On the same hour of the same day can also have a possible interpretation though a bit imaginary as I don't know that whether its possibe or not-

A gap or difference of exactly 12 hours

For example- 2 a.m. and 2 p.m.

Otherwise I would have gone wid the earlier replied answer that "same day" does not mean the "same date of the same month"!!!

They might also be two of the triplets, quadruplets, etc as earlier answered by someone.

Another possibility could be that one or both of them are adopted(as there is no clarification).