https://www.pcgamer.com/destiny-2-reworks-nightfall-strikes-removing-timer-and-adding-challenge-cards/

Bungie plans to remove the timer from Destiny 2's high-level weekly Nightfall Strikes and rework the scoring system to encourage players to kill more enemies, it has announced. The current system, which kicks you out of a Nightfall strike if you go over the time limits, "pushes players through the encounters as fast as possible" and "turns a lot of people off", Bungie said in a blog post.

So, the team is reworking the strikes across a series of future patches to create a new scoring system that lets players take their time if they want to, and rewards every kill. Your score will be the sum total of your team's individual points, and the easiest ways to ramp it up will be killing enemies and generating orbs by popping your Super abilities.