The demand for blueberries in the modern world doesn't disappear once they are 'out of season'. Like all produce however, the price does have a tendency to increase and at times sky rocket in the off season. Restaurants still need to serve their favored dessert and grocers will stock them so long so they are available.
Somewhere on the planet it's still the 'in season' for blueberry lovers, but the cost of shipping them from their point of origin, not to mention damage during transport, to the consumer is an obstacle.
Traditional greenhouse produce has a tendecy to be of a lower quality than farm fresh conventionally grown fruits and vegetables, but that is not neccesarily the case with hydroponically grown food. Properly grown and cared for hydroponic blueberries are equal to and in many cases of higher quality than those grown in soil.
An adventerous entrepeneur or even a hydroponic hobbyist can readily produce sizeable quality blueberry harvests over an extended season so long as they are willing to excercise due dilligence in maintainence of the plants and system in which they are grown.
Chilling Off Period - Dormancy
No blueberry plant will grow and produce continuoslly 365 days a year, they all require a period of chilling, similar to cold stratification, as is done with seeds if you are at all familiar with that.
Blueberries bushes are perennials, various cultivars that are bred or are indigenous to certain regions have varying chill requirements, referred to as chill hours, it is a dormant period. Chill hours are the total hours the plant is subjected to temperatures below 45 degrees F [But not much lower tha 32 F for any length of time] as they would be if grown outdoors. Without a dormant chilling period they might still produce for a period, but their performance will be drab and disappointing and the plants life expectancy diminished.
In addition to the lower temperatures, if you are still keeping them indoors less light is also advisable. Blueberry bush are cued into dormancy not only by the cold but by the shorter day length to prepare for winter . If you are moving them outdoors - disregard.
Chill hours variy amongst different cultivars, anywhere from 350 to 700 hours. As a rule of thumb use the USDA zones they are suggested for as basic guideline. Cold Hardy Blueberries that will grow outdoors in Northern climates, such Northblue, Polaris and Chippewa will need a longer chill period while those suggested for warm Southern weather such as Misty, Sunshine Blue or Ozarkblue require shorter chill periods.
Assuming that your plants are grown indoors in a controlled environment, it is possible to have some bushes' chilling' for several months while others are active and producing.
Why they are chill hours and not months or weeks ?
Horticulturists, Botanists, agronomists like to get overly technical at times, in my opinion anyway. Chill hours are referred to as such because they are not actual hours they are combined into a ratio / algorhythim that equates 1 hour of cold exposure at 42 degrees F to 1 chill unit or chill hour, while an hour at slightly higher temp. would equate to some fraction there of.
Chill hours are not written in stone, some variance is just dandy so long as you use common sense as described above. The suggested USDA zones for any cultivar in question should give a basic idea of how long the plant should be allowed to remain dormant or chilling. Plants grown outdoord, or in nature do not experience precise chilling periods every season sometimes spring comes early, sometimes late. Sometimes Autumn comes early, sometimes late ....
Rotation and acclimation
When preparing to rotate your plants to or from dormancy cut back on the nutrients, to about 1/3 the standard you have supplied them with for roughly 2 - 3 weeks. Do not send them from a warm environment to the chill temperature all at once, it is best to do it gradually over a period of several days so as avoid shocking the plant. If you are moving them to an outside environment the process of acclimating them and coaxing dormancy is pretty much the same as hardening off seedlings, but in reverse.