ok, five days is up (well, actually almost six days, lol). i have not done a water change in between putting the carbon in the filter on May 28th and today, as water change day was the day i put the carbon in. the water change i did prior to adding carbon was the same as others, about 50%.
result: slightly hazy water due to me not rinsing the carbon quite enough. this haziness resulted in me not being able to see if the carbon helped with TDS (total dissolved solids). nitrates are lower than they would normally be this many days after a water change. nitrates are closer to the 15/20 mark rather than the 30 mark, with 30 the norm for about 5 or so days after water change day. the filter floss on both filters was changed when the carbon was added. i did not change any other variables in the tank. fish behaviour, etc stayed the same for the duration of the experiment.
so is it worth it to run carbon all the time to keep your nitrate level lower, as per the article? for the result i got on my cichlid tank i don't believe it was worth it for me, as the nitrate level did not change enough for me to warrant the need for it to be in my filter at all times, and that would add an extra cost to my fishkeeping, without improving things enough to warrant the cost.