I guess that it depends in many factors like lighting temperature, moisture, the kind of geraniums you have.

for me i just dipped the cuttings in some rooting hormone and watered the soil well.
I did not cover them or anything just put the cuttings outside in the balcony and in two weeks i could see roots at the bottom of the pot when i took the plant out with the soil.
two more weeks and the roots filled the pot and the geraniums started to make new growth.

i found out that in general geraniums are easy to root and do it in a short time.

this is when compared to another plant , Brunfelsia that even now after a months is just starting to show signs of root dots.

The big no no is keeping the cutting too damp. Geraniums cuttings are particularly prone to rotting. Council of perfection is to leave the cutting out in the air for a day or two before planting so the cut end can callous over. That helps prevent rot. Keep the medium fairly dry. Some bottom heat doesn't hurt.

Came here to say the same thing re leaving the cuttings out 24 - 48 hours to dry out the cut end before dipping in powdered rooting hormone and setting them in the pots.

Leave them until the end starts to shrink and shrivel. Makes a huge difference.