Typically plants in pots will bloom earlier as their soil heats up faster than those planted in the ground. Introduce them to light slowly (put in bright shade first, then put out into bright sunlight a day or two later). I have had foliage buried under leaves green up after a few days of being a bright chartreuse.

I'm not certain you can avoid this happening in the future. You might consider trying to insulate the soil by wrapping the pots, but it probably will still bloom earlier. Just check them more often and maybe don't use a black bag.

Maybe what you mean is that the leaves and flowers are pale colored because they didn't get a good amount of light. You can just harden them outside (weather permitting) and next year they should be fine.

Do you mean that you want to grow some in pots next year as well but you don't want them flowering too early?

If so, then you could 'plant' the (planted up) pots in the garden, instead of putting them in the garage. The surrounding soil will keep them cooler. Then you can pull the pots up and take them indoors when desired.