I'll assume the geraniums were not cut back --either before they went to the window or afterwards.
Now's the time to do that....cut them back --4", 6", is a good size to begin their new year of growth and flowering.
What is suggest here can be done year after year after year to keep those geraniums coming back every time.
I have 7 plants....5 of them are at least 5 years old....that I remember, the other two were repeats from two years ago. I have them in west and south facing exposures as I write.

Cut them back, clean away any damaged or weak branches, any old flowering--they are not ready to push flowering at this time so get rid of the old and prepare for the new.

Into a clean pot, fresh potting soil, (put something between the soil and the drainage holes so that soil cannot plug up the holes) and place your cut-back plant in, firm it up, water it to drainage, allow full drainage, then dump the excess in the saucer below. Don't allow water to sit longer than 10 minutes while its draining otherwise it will be sucked up again around the roots which just got rid of it. Now, no more water until new growth appears, then water only as the plant needs it.

Take to a sunny window...south, west, or east is ideal.
Turn the pot every other day to ensure all parts receive sunlight. It will be about 10 days before new growth is seen and more every day until it assumes full foliation.
Don't be concerned if flowering doesn't appear while indoors...it will come as the sunliight encourages it.
Put it out of doors when temperatures allow it....back indoors at night, back out during daylight hours and longer each day to acclimatize when it will go out to stay.
Every time you water, water to drainage, dump the excess.
Use your finger to poke down to test whether it needs water....don't overwater.

Granny, pinching refers to the act of removing the flower heads of the geranium which wishes to produce many flowers and the old ones drop petals and otherwiss look dismal.
Pinching....put the fingers on the stem under the flower and follow it down to where it junctions at the stem.
Pinch with themb and forefinger. This gets rid of old, tired flowers and encourages new flowering by saving energy.
Flowering is the one biggest energy user on any plant so if you can get rid of the old, it gives more energy to producing the new.

I'd forgotten to ask in the previous post whether the plants you have now are showing signs of growth...spindly I'd say probably, maybe giving you the impression they are growing and should be encouraged at this stage.
Its the sun's fault. The winter sun is not capable of encouraging new growth--its intensity is very low and is the reason why plants go into dormancy--sleeping the winter away. When there is sunlight on a plant, and you give it water, it is encouraged to grow as it can but the winter sun is not sufficient to encourage strong growth.
So weak growth happens, spindly branching and stems which will fail if you let it remain. Better to cut it back to strong stem and branching and let the plant grow anew with the coming stronger sunlight. That starts about the middle of February but the ides of March is a good time to bring plants out of dormancy and encourage new growth in the stronger sun.

I am hoping that I am not too late to consider this, but ....
It is now April 19th, and our frost free date is June 1st. I have over 100 geranium ( pelargonium ) which are potted up and blooming under florescent lamps.
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As you can see, many of the plants are in full bloom, but are getting too "leggy" due to the artificial light. I am thinking that I should be cutting them back to about 4 inches in height.

My question is, is it too late to do so?

Where would be the best place to make the cut? Above a leaf node?

Is it too late to start more cuttings with what I cut off? I am really kind of cramped for space, as I have about a hundred dahlias coming along now, and a few hundred annual seedlings as well.