if ure going to use 12.5 mcgs, i suggest u use it before bed, that way u get to have t3 in ur system when ur metabolism is most likely to be at its slowest... half life of t3 is less than a day, so its generally split into 2 doses, but like u said, u cant possible be realistic and try to use 2 doses of 6 mcg each...
one more important thing though, your own body itself makes around 20-25 mcgs t3 when your system is healthy, so where's the point in taking 12.5 mcgs? take 25 atleast is my suggestion...