DIAGNOSIS The filter reminder isn't based on time, it's based on the number of cycles run. If you run a lot of quick cycles, it'll trigger faster. Also, if the filter wasn't seated perfectly when you reinstalled it, the sensor might not recognize it as 'clean'.
FIX You need to manually reset the reminder light. With the door closed, press and hold the "Sani Rinse" and "Normal" buttons simultaneously for about 3 seconds. The "Clean Filter" light should turn off. If it comes back on immediately, the filter assembly isn't seated correctly. Take it out and reinstall it, making sure it clicks and twists fully into place.
IF THAT DIDN'T WORK There's a small magnet in the filter cover and a reed switch in the base. If either is damaged or covered in gunk, the machine can't tell the filter is in place. Clean the area where the filter sits and check the small plastic nub on the filter cover for the embedded magnet.
HEADS UP Don't ignore this light thinking it's a glitch. A poorly seated filter can cause poor cleaning performance and even damage the pump.