It really depends upon the area and if the plants are indoor or outdoor. Blue colored flowers are a sign that the plant is mature and will produce fruit within about 6 months.
Change in color is the first sign that the pineapple is ready to harvest. The color toward the bottom of the fruit will become yellow first followed by the rest of the fruit. When the entire plant becomes a yellow/green color it is time to harvest.
Smell and firmness can also be signs of ripeness in pineapple. Test the fruit by thumping it with a finger. If it sounds hollow it may need more time to ripen. If it has a firm and full sound it is probably ready to be picked.