I also find the "dose macros in the morning and micros in the evening" a bit silly too. The PO4 will reduce a little during the day due to plant uptake, but it is not any 'less-effective' at precipitating Fe from solution in the morning or at night.
So levels of PO4 do fall during the day, but PO4 is very good at staying put in the water column. It's an anion, and little is lost to the negatively charged substrates etc, hence why phosphate is such a PITA in water treatment. It's difficult to get rid of it in comparison to other ions. Nitrate is similar although the famous 'denitrification' by anaerobic bacteria is our friend here if necessary.
Potassium (K+) is much different as a cation as an example, it's encouraged OUT of the water column. PO4 will stay in the water column of your tank for weeks (or months, or a year....), so long as plants don't use it or you remove it with a water change etc.
Add iron at any point and you'll get FePO4 forming immediately. Strength of chelates (and a mix of them) makes a huge difference in this regard. The Fe is held up 'in-prison' and the PO4 can't get to it. Overtime the chelates break down and the PO4 will readily start reacting with iron. PO4 may have been added 12 days ago, but it will still begin this process of reaction with Fe immediately.
If I had an auto-doser I'd dose Fe just before lights-on where the light assists in making it available to plants. This ensures that maximum Fe is available for photosynthesis. As I rely on doing it by hand, and I've done it for many years, I can't be bothered dosing daily, just every 2 days and macros + micros at once. PO4 will likely still be in there from your last dose (if non-limiting nutrients are your thing), you're just topping up, don't worry about when you dose it.
I followed the advice to avoid dosing Fe and PO4 together for a LONG time... then I got lazy and dosed them together and guess what... there was no problem. Nothing changed, plants looked exactly the same, strong red plants, no cloudy precipitation etc. It's been a few years now and I'm still lazy and everything still works just fine.