How do you set the clock on a JVC KD-R200 car stereo?

Try this.
Press and hold the SEL button. When the menu appears, if pressing left/right button doesn't select clock, try turn the volume to select and press right/left to set. Let me know it works.

Press and hold SEL (select) for more
than 2 seconds.
"DEMO," "CLOCK H," "CLOCK M," "DIMMER,"
or "AMP GAIN" appears on the display.
Set the hour.
1 Select "CLOCK H" (hour) if not shown on
the display.
2 Adjust the hour.
Set the minute.
1 Select "CLOCK M" (minute).
2 Adjust the minute

Hold the SEL button to bring up the PSM menu, use up/down to select CLOCK H for hour or CLOCK M for minute, turn the knob to adjust, and press SEL to set.
Full details are on page 3 of the manual.

http://books.jvc.com/Download/358948444/GET0582-001B.pdf

Here's the manual for your KD-R200:

http://resources.jvc.com/Resources/00/01/15/GET0582-001A.pdf

the settings and adjustments are found on the left half of Page 3 of that PDF.

I hope that works for you.

Press and hold the SEL button to enter the menu
Using the scan buttons (FWD/REV), select Clock H
Using the volume knob, set the value
Using the scan buttons (FWD/REV), select Clock M
Using the volume knob, set the value
Press SEL to finish

Press and hold SEL until menu appears
Using the scan button (FWD/REV), select Clock H
Using the volume knob, set the value
Using the scan button (FWD/REV), select Clock M
Using the volume knob, set the value
Press SEL to save and exit

Press and hold SEL to display the menu
Using the scan button (FWD/REV), select Clock H
Using the volume knob, select the valud
Using the scan button (FWD/REV), select Clock M
Using the volume knob, select the valud
Press SEL to save and exit

http://resources.jvc.com/Resources/00/01/15/GET0582-
001A.pdf

you will find the instructions on the link above

For the JVC KD-G200 look here for instructions on how to set the clock...

http://www.fixya.com/support/p187738-jvc_kd_g200_cd_player/manual-17158/page-9