Data point: entered 3/26 at DEL from US. Zero line at immigration around 8pm; similar for a colleague arriving from SIN the next morning around 6am. I had to show Air Suvidha form and my e-visa. Perhaps because I was on a business e-visa, not tourist, I had to have my photo and fingerprints taken by the immigration officer. All-in-all, 15 minutes from doors opening on the plane to departing airport. Very fast. Lines had formed after me, and from 3/27 more international flights will be coming, so my experience is likely no longer typical.