I have a casio 4798 model watch and the date changes at 12 instead of 24. anybody can help me? thanks

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)

You need to advance the hours (hour hand) 12 hours forward to have the date changed at 12 o'clock midnight.

A detailed description of this procedure is found in the manual of your watch. You can find the right manual with the module nr. on the back of your watch (4 digit number in a rectangle)

The manual for your watch can be downloaded via the link provided below:
Timepieces Watches

from the user manual press the button closest to the seconds display on watch . bottom right button in normal time display to switch between am / pm time or 24 hundred military time.
http://mygshock.com/casio-manual/548/
enlarge the internet browser display to read which button to press to change the time or date.
press button B top left button to go into change mode
press button C bottom left button to move to seconds or minutes or hours .
press button A bottom right button to advance the time
press button b top left button to go back to normal time display

How to Set Casio Watch

specifically step 6 below for your answer

Setting Instructions for Electronic Watches

Casio electronic watches feature many different modes ranging from timekeeping to stopwatch. The M button controls the modes. Here is how to set time on a digital watch such as models 1632 and 1813:

1. Press the M button to get into the Timekeeping mode.
2. Select the seconds digits by holding the A button down until the seconds digits flash on the display.
3. As the digits flash, press the C button, which will reset the seconds to 00. On some watches such as GW-500A, a stop/start button is used instead of a C button.
4. Press the M button and change the selection in the order of seconds, hour, minutes, year, month and day. Proceed in that sequence to change information to the current time and date.
5. As the sequence progress, digits flash when selected. Press the C or stop/start button, to increase a selected number or the B button to decrease it. Hold down either button to increase the speed of the selection change. All time and date functions are set this way.
6. Press L when any digit is selected to switch between 12-hour and 24-hour formats.

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.

I think this operation guide for your watch will be at help

http://wrzuta.hihawa.pl/casio/wvq570dbe.pdf

Regards

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.

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.

On the Casio 2747 you can easily change between 12-hour and 24-hour (i.e. Military time)... Follow these steps:

1. Make sure you are in Timekeeping Mode (i.e. digital display shows date at the bottom).
2. Press the "D" button (i.e. bottom-right button) to toggle between 12-hour and 24-hour timekeeping.

Note: 12-hour timekeeping mode will display an "A" or "P" for AM and PM.