David, I think it depends where you live. For example, our longest day here in Florida at this time of year is about 15 hours of daylight, whereas up in Canada they get nearly 19 hours of daylight in June. Sweden and Alaska - 22 hours plus! In winter, though, we have longer days than more northerly places.
There are some plants that are triggered to put on blooms by day length, like poinsettia but I've never heard of an annual that you couldn't bring along to bloom at just about any time of year with good growth and enough sunlight. (and of course minimum warmth at night through winter, such as a greenhouse would provide)
If I start Zinnia seeds in February, I can have them blooming by April, and keep them going as long as I deadhead them (remove the spent flower heads). Bugs or fungal infection kill them off eventually or a few cold nights in December. Vinca is sold here nearly year 'round and is somewhat perennial. It blooms off and on in winter, and all the time from March through November.
Perennial bloomers can be more light sensitive i.e. require a certain amount of sun to start blooming. But perennials like gingers which are labeled to bloom "late summer" are already in bloom for me here. It warmed up nearly a month early here this year.
Your climate and the varying seasonal warm-up and cool down will determine when your annuals will bloom for you.
