I have noticed that with a lot of heavy scented plants , they seem to hold the sent till just the right time.
If I may jump in here - The odor of blooms evolved to attract specific pollinators. The intensity of the scent will be strongest at the time of day that pollinator is around to do the job of pollinating. If you have a flower pollinated by a moth, your bloom will most likely be scented at sundown. Bee pollinated blooms might be mostly scented at day time and so on.
