i can't answer your question directly because your post was a bit hard to follow on what was his and what was yours and where you are going wrong, but I do know pharmacology.
I can tell you that is doesn't really matter that much and will be wrong because a day is 24 hours and there is alot of fluctuation going on.
Biomedically we are interested in blood levels sustained on an AVERAGE to get therapeutic results. This is WHY half lives exist and give the basis for when you dose. all of these are affected by the ADME scheme which can also change person to person and therefore why dosages are person dependant and start low and work up.
Honestly it is easier if you simply take out some graph paper and put time on the bottom and blood levels on the side. Your graph will then look like a stock exchange as it goes up and down as levels peak (but continues up at the begining) then sorta roller coasters while you stay on your dose. This graph is simple and can be done with the half lives and without crazy math.
if your obsessed with the math, please clarify where your problem is so i can look closer.