Creating Unlimited, Permanent Loyal Minions

Ok, so I come up with this idea while preparing for a level 20 one shot vaguely themed around Jurassic park. If anything I say here is incorrect, please let me know and if possible, correct me to how this could potentially work if at all.

So if I, a 20th level chronurgy wizard, wanted to create a couple of minions, could I cast a 4th level Summon Construct, then cast true polymorph on it to turn it into a creature of equal or less CR rating, that being CR 9?

My thought process is either make use of glyph of warding to cast the original summon construct spell or my subclass's tenth level feature, allowing me two concentration spells at once. Or is there a some ruling about true polymorph overwriting the original summon spell's duration/concentration? Either way, I should be able to cast both spells at the same time and, if my thought process is correct, have a permanent creature that's loyal to me and follows my commands.

The only real hiccup I can think of is would the summon construct still fade away, even if it's no longer that creature anymore once the original spell ends?

Curious to see if I'm hitting on something that could, in theory at least, net several minions without worry of them vanishing or losing control. It's not too different from the whole planar binding process (combining certain summon spells, glyph of warding, and planar binding).

Why would casting True Polymorph overwrite the duration of the original summon spell? Planar Binding is the way to go if you want long-term minions. Though if you just want a horde of minions the Horn of Valhalla magic item is a better choice since you don't need to worry about transporting your minions with you.

Worth noting, it would seem that the stat blocks of the various Summon X spells do not in fact have a CR. Ergo, they're not eligible targets for True Polymorph, having neither a CR nor a level.