Does cooking black bengal gram with salt lead to increased cooking time or lack of softening?
No, this is a common myth. If you want to test it, you don't "try once with salt", you divide the same batch of beans and cook them both, one with salt and one without, under the same conditions, and repeat. This is what a food author did, although he seems to not have repeated the experiment: http://www.seriouseats.com/2016/09/salt-beans-cooking-soaking-water-good-or-bad.html. His salted beans were somewhat better than the unsalted, and he states he now always cooks them in salted water.