I don't believe there is any benefit to a "rest" day. Instead, I prefer to just alternate macro and micro dosing. When I do water changes I dose after the water change, with whichever is scheduled for that day - the one I didn't dose the day before. If you want to save fertilizers, just do some testing to optimize the dosage sizes. (Reduce one nutrient dose slightly, and watch to see if the plant growth is adversely impacted. If not, reduce it slightly again and watch for adverse effects. Keep this up until you can see an adverse effect, then go back to the previous dosage, and start the process on another nutrient, until all have been reduced appropriately.) As your plant mass increases you will probably need to nudge your dosages up a bit to supply the higher demand.