The general consensus on when to take anastrozole is on the day of injection. If you’re pinning twice a week then taking your AI twice weekly should be sufficient. The half-life of anastrozole is ~3 days, which doesn’t mean that it’s effective life is three days. Twice weekly should be fine.
There are two schools of thought when it comes to starting an AI. The first and most common thought is to take it from day one. Anastrozole takes seven days to reach peak blood plasma levels, so you’ll be building to that while the testosterone esters are breaking down and releasing into your system.
Thought group number two is a little more cautious. This thought is to start the anastrozole at a lower dose at the beginning and then dial in as you go. I’m in this camp because I know what a frozen hellscape life is when your e2 is crashed. I prefer the flexibility that you get when you start lower, get your body used to the new drug, then tweak dosage as needed. The truth is more muddy though…because without blood work you won’t actually know anything for sure. So if you’re doing it by feel then I say start lower and adjust. If you’ve got blood work and you know what your baseline is going in you can probably make a more accurate estimate of dosage and timing.
You don’t need an AI when you’re into pct. Because you’re not feeding your body exogenous testosterone you shouldn’t have an issue with excess test aromatizing.