@NoWaiAma Generally a little bit of sitting unused is no issue. Extended period of more than a few weeks can run the risk of allowing bacteria to develop on the membrane. Biofouling can be an issue, so I generally recommend running the unit, even if just for a little bit, at least every couple weeks.
Volume of water processed will be a bigger factor than time. Sediment filters will vary a lot based on your water, as some people have more dirt in their water and see the sediment filters clog faster, while others have very low sediment water and see very little pressure drop. Pressure loss will dictate when to change the sediment filter. Chlorine/chloramine getting past the carbon blocks will tell you when to change those out (this can be tested with some basic free + total chlorine test strips). Carbon blocks will be affected more by the volume of water processed, as their capacity for chlorine/chloramine removal is somewhat fixed. The DI should be changed out when the color change is at about 90% or you begin to see any TDS breakthrough on the final line.
To play it safe, many people will replace the pre-filters every six months or so, but ultimately keeping tabs on the performance of each filter is the best gauge.
