To reset your NVRAM, you use exactly the same procedure you once used to reset PRAM.
Shut down your Mac.
Press the power button, and as soon as you hear the startup chime, hold down Command-Option-P-R.
Keep holding down those keys until you hear a second startup chime. Then let go and allow your Mac to continue starting normally.
Then check the Startup Disk, Display, and Date & Time panes of System Preferences to make sure they’re set the way you want them.