In a few weeks you should begin to see roots coming from the bottom of your cutting. Also, rosemary roots quicker if the cutting is resting on the bottom of the jar, not floating. Be sure to change the water every four or five days.
Rose cutting method by flowerpress, via Flickr ......I will try this method soon!!! With the potato method, I was able to grow potatoes, but not rose cuttings. ~sj