During the fall-winter time usually it takes months to grow some poor roots on Sansevieria. And some types do this much slower than other in my expirience.

Actually right now I have one Kirkii leaf in water for 4 months, and still nothing.

Growth powder.

I never callus mine. I trim my overgrown ones with a wide "^” shape (upside down 'V'). I stick them in a jar of water like yours and let it face the sun. Occasionally refill the water and rinse if necessary -- sprouts roots like crazy and even further sprouts. Fun fact: they thrive in water!!

I’ve got some sitting in water in my kitchen that have been there for the past six months. They only started putting roots out after about four? It takes a long time!

I just stick them in dirt and water it. They end up growing but they do take a little while.

They take a lot longer than 2 weeks to begin rooting, in my experience. But if you leave them in the water they'll root eventually.

As a side note, the babies will not have yellow leaf edges. This type of sansevieria reverts to an all-green variety when propped this way. If you want to keep the yellow edges, you have to prop them by letting them bud off the main root.

Lay them flat on potting soil, mist from time to time, they won't usually root in water.

The idea is to mimic the natural process where a leaf will break and fall on the ground to take root