I assume most are showing total travel time. NYC-Europe-India can nominally be two 7-8 hour flights with a 3-5 hour layover between, so that can be 20+ hours total.

On many websites, the flight options are ranked by ticket cost, and if there are multiple flights from NYC to the connection point, earlier departures from NYC might be cheaper than later ones, hence you're seeing 24-hour trips high up on the list.

Could some of those options also involve arrival into BOM or DEL with an onward leg to MAA with same flight number? That will add some hours as well but might not show up as an additional flight leg.