Assuming you have a JVR 212T, here's what the owner's manual says:
• Press the power VOL/ button (1) to turn the unit on/off.
• Press and hold to turn the touch screen backlighting off when driving at night. Audio playback
is not interrupted.
• Touch any area of the screen to resume the previous display lighting and mode
In my 2014 Vegas, I had to install an on/off switch to get the unit to completely turn off, i.e. no clock. There are good instructions in exactly how to do it somewhere in this forum. It is not hard. Take out the radio and cut one wire and splice the switch in. Mine was tied to the house battery and was a significant drain while dry camping.