Correct, and not to hijack but Congrats, Anthony!
To be safe, I dose them about 5mins apart after the WC. Some folks don't even do that, they just dose on either sides of the tank.
This is really more of a concern if you are making dosing liquids. Then of course, you wouldn't want to mix them together.
I will say this; I dose lots of Fe and I did once turn my tank water into milk. That was my fault though, I dumped them in the tank after a WC with no pumps or filters running and to top it off, I dumped them right ontop of eachother...
Iron and phosphate will form iron phosphate, but this really only occurs to any large extent in concentrated solutions.
Given that we are dosing small amounts of fertilizer and they are diluted rather quickly in the aquarium, the chances of iron phosphate forming are lower (still possible, however).
I think the one day where the macro and micronutrients are doubled up is fine.