Flowers stay in bloom for such a short time every year here in Canada. We seem to get them starting to come out in late April-early May, then by September most of them will be withered and gone for another year. I find I can enjoy them all year round, though having so many macro images of them.
The purple and violet lilacs are around for anywhere from 2-4 weeks on average so their time is very fleeting. We have an annual lilac festival here that occurs during the height of their season. I find the aromas to be very pleasant, and they are often the type of flower where you could simply be walking by and get a great whiff of their light aromas.