I installed an aftermarket stereo in a 2018 Nissan Sentra. Stock stereo adjusts time.How do I adjust my dash clock without the stock stereo?

Answer 1

Simple. You can’t.

If the stereo head unit includes a time display then you use that instead.

Answer 2

You're lucky. Many Nissan's and Infiniti's run the climate controls through the stock radio and when you remove the stock radio the climate controls will not work to give you heat, AC, or defrosters.
Have you tried the heater yet? You might be in for a nasty surprise!

Answer 3

read the manual, follow the instructions