There's much more to a steroids active life and half-life than the number of days to half the blood concentration. In a simplistic exaplanation, just looking at 600mg of Enathate with a half-life of 8 days would give us the following:
8 days 300mg
16 days 150mg
24 days 75mg
32 days 37.5mg
40 days 18.75mg
48 days 9.375mg
Consider than 100mg is a standard hrt dose and would yield a reading of around 500 or so which is average, we might/should consider than the level where recovery can start to happen as it dips below natural endogenous levels. So going with this common train of thought we are looking at around 21 days to 100mg (many other factors to consider, but let's keep it simple for now). Another thing to consider is that when using compounds like Deca which cause a complete suppression at 100mg and even lower, and with its longer half-life, even at 4 weeks out you are unable to reach full recovery and is part of the reason that I and others recommend stopping most all compounds other than test at least 2 weeks earlier than your test so that it/they can clear and you can gain recovery before you stop your PCT. Many people in my opinion/experience start pct too soon and/or stop to early and are only, let's say, 75% recovered, which can be fine as the body will recovery without pct drugs given the means and the time.
By the way, I personally would recommend, as far as pct goes, to run your AI 2-3 weeks past your last shot and then start your serms. The 'just in case' factor is covered as AI's tend to increase testosterone just as well as SERMs though not in a healthy way. A sample would be to run the AI 3 weeks past, run Proviron 6 weeks past, and the Serm 9 weeks past (for a total of 6 weeks)
week 01 ARIM PROV
week 02 ARIM PROV
week 03 ARIM PROV
week 04 ----- PROV NOLV
week 05 ----- PROV NOLV
week 06 ----- PROV NOLV
week 07 ----- ----- NOLV
week 08 ----- ----- NOLV
week 09 ----- ----- NOLV