oh, man, i was gonna say more than that! doh!
i was reading somewhere the other day that its the bottom inch of the r/w cool that dries out the most. so if the top of the cube is drying out the bottom probably already is dry. Its common sense but its worth keeping in mind.
Dry is good for plants, but not for too long. the roots crave water!! and i just think your cubes look fairly dry (that could be because they are different to the ones i know of though!)
just trying to help mate
ps: i think your plants are going do just fine!