Why does date index at 12:00 noon instead of 12:00 AM?

Time is not set correctly. You set the time as AM instead of PM and vice versa. Use the following manual to set time correctly.

QW-5479 (casio.com)

probably because you have it set to 12 pm midnight and not 12 noon so at 12 noon it is actually midnight when the date will change
reset the time of the day to am or pm and any pm settings will change the date at 12 midnight.

Hi.
I take it that your watch changes date at 12 noon, instead of 12 midnight.
If so change the time of your watch 12 hours, so it reads the same time, but instead of am, it is pm, or visa versa. Analog watches do not have a 24 hour time setting.

Hi!

The problem you described is caused by incorrect setting of the hour: AM and PM must be set correctly, AM before noon and PM afternoon.

For more details regarding setting of your watch, please visit Citizen site here:
http://www.citizenwatch.com/COA/English/settings.asp

Please let me know if it helped,

good luck!

So to change the Day and Date of your Watch, slowly pull the Stem out... (Do note that if you have a Waterproof Watch, you'll need to unscrew the Stem counter-clockwise, which is towards you, until it unlocks, then you can pull the Stem out!) But this is where you need to go slow. If you pull it out slowly you should hear one snap. (It stops on the first notch) If you pull the Stem out all the way, it snaps twice and ends up on the second notch. (See picture below) The second notch, or all the way out, is where the Stem needs to be to set the Time.
But the first notch, or first snap, is the secret and the key to setting the Day and Date! In the first notch position, you'll see that if you spin the Crown one way, it will change the Day. Spin it in the opposite direction and it changes the Date!
Do keep in mind that you may have to spin the Day and Date a couple rotations because it most likely will alternate between English and Spanish. Just pick the correct Language for you and it's done! When the Day and Date are set, push the Stem in all the way and enjoy your Watch!
If you still have the problem with your Watch changing Dates at Noon instead of Midnight, that just means you're on the wrong 12 hr cycle. (It's set for Twelve at Night instead of Twelve at Noon) All you need to do is pull the Stem all the way out, (second notch) and Spin the Minute and Hour hands ahead 12 hours. If it's Twelve O'Clock, spin it ahead until it's Twelve O'Clock again. Doing that will put the Watch on the correct 12 hour cycle.

Your watch is 12 hours out of step. (The date changes every second revolution of the hour hand.)

Wind your watch forward 12 hours, (you may have to reset the date) and it will then change around midnight.

But the first notch, or first snap, is the secret and the key to setting the Day and Date! In the first notch position, you'll see that if you spin the Crown one way, it will change the Day. Spin it in the opposite direction and it changes the Date! Do keep in mind that you may have to spin the Day and Date a couple rotations because it most likely will alternate between English and Spanish. Just pick the correct Language for you and it's done! When the Day and Date are set, push the Stem in all the way and enjoy your Watch! If you still have the problem with your Watch changing Dates at Noon instead of Midnight, that just means you're on the wrong 12 hr cycle. (It's set for Twelve at Night instead of Twelve at Noon) All you need to do is pull the Stem all the way out, (second notch) and Spin the Minute and Hour hands ahead 12 hours. If it's Twelve O'Clock, spin it ahead until it's Twelve O'Clock again. Doing that will put the Watch on the correct 12 hour cycle. Granted, you may have to reset your Day and Date again since you just advanced it, but at least you'll be in the correct Time Zone! Happy Spinning! google_protectAndRun("ads_core.google_render_ad", google_handleError, google_render_ad);

mcdevito75 here, Many Casio Watch Models out there, I'll bet however your Casio is displaying say 1 AM rather than 1 PM as it should if the time is indeed PM after 12 noon, if so, this is why the date is changeing at 12 PM rather than, 12 AM simply re-set your casio and make sure the time of day is set at PM for time after 12 noon and AM for time anywhere before 12 NOON. Also, as you set your Casio, look for anything that may give the hint of Military time, this may be revilled as 12 hours or 24 hours, if you have anything like this, make sure it's set for 24 hours. If you have additional problems, visit a small watch repair shop in your area. Again there are many, many Casio models out there and without your watch with me it's difficult to be more accurate.

NOTE: NEVER EVER set the date between 7pm and 2am or you will damage the watch!! The crown is screwed down to make it waterproof. Start by unscrewing the crown by turning it counter-clockwise until it pops out slightly. That is position '1' which is used for winding. Pull it out two more clicks to position '3' and set the time by turning the crown clockwise. Turn it past midnight at which point you will see the date change and continue turning till you get to the right time. If you're setting the time to a point after noon, be sure to go all the way past 12 noon before setting the time or the date will change at noon instead of midnight. If the time is before 7pm push the crown in to position '2' and turn it to set the date. When you are finished push the crown all the way in and turn it clockwise to screw it down.

If you dial in the date before noon make sure you stop winding the crown right after the date flips. That will give the internal mechanism the most room to cycle and not flip at noon. If you are setting it after noon wind the crown just until the date you want starts to move to the following date, but stop immediately after so as to not flip over. That way the mechanism will be close to changing the date and should flip it at midnight. Make sense? Hopefully, good luck.