I assume you mean A syriaca (but best to be precise, so people don't have to assume). It has a reputation of being incredibly tough and spreading rapidly. Given that the pot don't freeze I feel it likely it will make it.

I doubt you're any more likely to overwinter them in pot (which can be tough with milkweed...too wet) by starting earlier or not.

They will take several years to reach maturity (or that's my experience), I expect some flowers from past years planting (as young plants) in 2023. Of note, if not in full sun, they mature MUCH slower (5 years and counting...but each year they get bigger). In full sun, I estimate 3 years to maturity.

Milkweeds are weeds. Mine have lost their leaves. I have no doubts about their health. They are growing bigger and thriving more each year (except if I toss the damned things). IMO, there are prettier plants to grow. If you're dousing them in neem or other pest repellants, you're going to repel or kill any Monarch caterpillars, too. So, unless you love the look (which I kind of doubt) or if you're doing it for the Monarchs, I'd plant something else. Zinnias and Cosmos will attract Monarchs. Monarchs will visit many other plants and anything that kills aphids isn't good for caterpillars, so you're doing nothing for them that another plant won't do.

I have some pearly everlasting, which is a host to Painted Ladies, which look kind of like Monarchs. Their blooms last a long time and I've had caterpillars pupate on my stand. It's another weed, so it thrives.

Thanks...yeah...I'm doing it for the Monarchs, but seeing as the plants were a mere 5" tall and had only germinated a few months prior, I can't imagine there would have already been opportunity for Monarchs/eggs on my plants?

I didn't realize that other plants are also host plants for Monarchs? So why all the talk about Milkweed, I wonder?

They're not. Only Asclepiads are host plants and Monarchs perfer certain ones of those.

Monarchs DO lay eggs on young seedlings. I would stop applying neem which will also kill adult butterflies and any other insecticidal soaps or other aphid killers. Just spray the aphids off with a hose. The milkweeds always drop their leaves at this time of year anyway. There's a good chance they will return next spring. If you know anyone with established Asclepias syriaca plants, see if they would share a division with some tuber attached. It would speed up the process. Milkweed roots need a lot of growing space, so consider planting the seedlings into the ground earlier in the season instead of keeping them in pots for an extended period.