Pesachim daf 2 - Ohr = day or night

I'm wondering why this gemara begins with a discussion of whether אור means day or night. I think it's interesting that this kind of issue comes up so much on Pesach.  The mefarshim talk about how the night of the seder is unique in that it has lots of special mitzvos, more like the daytime of any other yomtov. And the korbon pesach is brought by day, but very late day (בין הערבאים), after the time of almost any other korbon. The gemara here comments on the unique division of the day of the fourteenth into before and after chatzos, with regard to the issur of chametz.
Maybe someone has other ideas about this or other examples?