I never thought about fragrance chemical change, and I can't say I have ever noticed a difference, other than intensity. I could be wrong. I really should be staying out of this conversation, due to my "handycap", but.....
It is well documented that with some other flowers will exude their odor more at a certain time of day. It always seems lilies in general are more fragrant in the evening, but that may be because the winds are always more calm.
