The Nikon Coolpix L820 cannot shoot a true still-image time-lapse. It does not have a built-in intervalometer, and it also lacks a shutter release port for connecting an external intervalometer.

So there aren’t any camera settings that will make it capture one frame every few seconds or minutes for a sunrise/sunset sequence.

Your practical workaround is to record normal video and then speed it up in editing, or remove frames in post to create a time-lapse-like effect. That won’t be the same as a traditional interval-shot time-lapse, but it’s the closest option available with this camera.