The hyacinths need to be checked to see if they are ready to come out of the dark. The bulge of the flower needs to have moved out of the bulb. These seem to be ready. I'm surprised I have so many (18) ready to come into the light when they were started so late.
Even though the general length of time to keep the hyacinths in the dark initially is 12 weeks, it could be less. Check the bulbs and go by how they look. Of those first 18 out of the dark, 3 have been in the dark for 7 weeks, 9 have been in the dark for 8 weeks and 4 for 9 weeks.
Of the first 18, 7 are Anne Marie (usually the first in bloom), 5 Pacific Ocean (I haven't used these before but seem to be early), 2 Delft Blue, 2 Sainsburys, 1 Splendid Cornelia and 1 Caribbean Dream.
the hyacinth flower can be seen between the leaves of the emerging stem, the others will be similar even if the flower is not visible, the shape of the stem shows the bulge of the flower
these hyacinths are not ready to come out of the dark yet
these hyacinths are not ready to come out of the dark yet, although the one front right is on the edge
As well as checking the hyacinth bulbs to see if they should be taken into the light, they should be checked for water levels but I find they generally don't need topping up. The vase below is typical. The bulb has acted like a plug to prevent the water evaporating
the more open vases have evaporation, I topped up the square vase on the left which had gone down to half full, it also shows the different growth rates of different bulbs and the problems of containers with more than 1 bulb, some bulbs are ready, some are not
I've brought those 18 hyacinth vases into the house. If I put many more on this windowsill Victor (or any of the other cats) won't have room to sit on it. The hyacinths really shouldn't be by a radiator but I have limited space.