I have a Philip Persio watch which has Day/Date display. In the Day display window it shows "LUN"...what is that??

LUN is French for MON - so either learn the French terms or find the manual

I assume you are talking about a day-date Timex. Timex watches do have a quickset feature meaning the day and date can be set without having to simply advance the time by 24 hours to adjust the Day-Date. Not all watches have a quickset, but I'm sure your Timex does. Unscrew the crown from the stem by turning it counter clockwise until it is free from the threads. At this point pull the crown all the way out so that you can adjust the time. That's position 2 the quickset is in position 1 but the tricky part is getting the crown in the proper position to engage the quickset. Push the crown in very slowly while turning once you see the day or date window advance stop turning you are in position 1. Day and date can be set in this position by turning the crown in either direction. If your watch does not have a quickset or you cannot figure out how to engage it you must set the date by advancing the time forward 24 hours. This will make the date window advance by one day. Once the right date is displayed turn the time backwards 24 hours and this will cause the day window to move without affecting the date window. And that's all there is to it.

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If the day is in a window next to the date, pull the crown out one position to the same position used for the date correction. Often turning one way changes the date, turning the other direction changes the day. If your day is on a small dial on the watch dial then pull the crown out two clicks and go around 24 hours at a time and you will see the day advance.

mcdevito75 here, The stem has 2 positions, first adjust the day or month by going thru the 24 hour cycle with the stem. once set, slip a finger nail just ubder the stem and lift carefully this should allow you to change the DATE adjust to 1 date before the date you need, now pull the stem out to adjust date and time of day turn sten the complete 24 hour cycle to achieve the correct date and time of day. Now your watches day and date are set and will change to the next day date on time, around Mid nite 1 --2 AM.

many of these watches require 2 batteries. One for the analog and one for the digital. I would contact a jewelry store to make sure they will change your batteries; since the watch was free to you it will surely be worth the price of new batteries to get it working.
Also, some models do take only one battery but if it is not at a full charge you may have the issue you described.
If not a battery issue, then there are other detailed steps to follow (the jeweler should be able to help you.)
Note: I recommend contacting an independant jeweler (non-chain and non-mall store) because most non-independants will not change batteries in watches they don't sell.

Hi Jeffrey, Put stem into "set hands" position and adjust hands to the 12:00 position. Day and date should advance at or close to that time. If you pass 12:00 and there's no change continue rotating another 12 hours and they should advance. Once youv'e found that there's midnight so if you're setting the time at say four (4:00) in the afternoon (pm) you will neew to rotate the hands so around the dial so they pass 12:00 once more then four hours more to 4:00. Now I assume by bilingual you mean that the day ring has like Mon (monday) and Lun for Spanish or the like. In this case if it's showing the wrong languare set the crown (winder) to the first position (second posn is "set hands) and rotate winder eithr clockwise or anticlockwise. Once you discover how to advance the day ring just set it to the correct day/language you want and press the crown home. Hope this solves your problem. If the advances are changing at some obscure time like 8:40 or something it's because the hands pave been located incorrectly and would need correcting by removing movement from the case.

On mine the back turns off using the notches in it. I persuaded it with a small screwdriver. Just be careful it doesn't slip and hurt you.

Press the lower left button and hold it there. It will stop the display cycling mode

(I'm dutch, so I'll try in my best englisch)

I don't know if you still have the problem, but what you should do is te following:

* pull out the knob (2 times) and turn anti-clockwise to change the time
* keep doing until it's 24.00 (midnight) and you day change's to the UK (!) day.
* push back the knob (1 time) and change the day to the FRANCE (!) day by turning anti-clockwise
* pull out the knob again and turn anti-clockwise to change the time until 03:00 (midnight)
* you see the then change the day back to the UK day

So, every night at 00:00 the day changes to the FRANCE notation and at 03:00 it then changes to the UK notation, so you can enjoy this setting during the day.

Good Luck.
Also owner of JR9589 watch.