The elimination half life of Arimidex is 50hr or so, not 6hr. It might take 6hr for the full dosage to be distributed through the body I guess. The drug very significantly reduces E2 levels in just 24hrs. Levels remain at a steady-state after a couple weeks of daily dosing in women. Levels recover after a week without the drug.
With HRT test and .25mg Adex EOD I have maintained steady mid-normal E2 levels for over a year now. I've had E2 checked over and over and over in that timeframe. There's no reason to split Adex up through the day.
I'd use proportionally similar amounts of Aromasin as Adex. Testing for E2 after 2wk of Aromasin, and again 2wk after any dosage adjustment, will tell you definitively where you need to be.
Do not over-suppress your E2!