Wait. One to four weeks depending on humidity and temperature. The putty should form a firm, dry "crust" on the surface. Then you prime and paint, lapping the paint 1-2mm onto the glass to create a waterproof film over the putty-glass edge.
Glass window putty plays a vital role in maintaining the integrity of our windows. Here are just a few reasons why: glass window putty
Here is the single biggest killer of putty jobs: glass window putty
This usually comes in a caulk tube or a tub. It looks and feels like thick white frosting. glass window putty