How do I know when it is time to replace the Pre-Filter vs. the HEPA Filter?

When the Filter Reset Light illuminates (solid, not blinking), it is time to replace the Pre-Filter. When the Filter Reset Light blinks every 2 seconds, it is time to replace the HEPA Filter. As a general guideline, the Pre-Filter should be replaced every 3 months and the HEPA Filter every 12 months. (Page 6-7)