When can you cast the instants copied by Chun-Li, Countless Kicks?

[MechaPsyche]

Chun-Li, Countless Kicks card text reads "When Chun-Li attacks, copy each exiled card you own with a kick counter on it. You may cast the copies." but 'you may cast the copies.' seems really ambiguous. There are a few ways I could see this being interpreted. My first assumption was that when this triggered ability resolves, you can pay for any spells you want to cast, put them on the stack in your chosen order, and the rest disappear. On the other end of the power scale, since it doesn't say that the copies disappear I wondered if you could cast the copies anytime during the rest of the game (when you have priority).

Looking at this article, they claim that you can cast the copied cards until end of turn, but I could not find anything in the comprehensive rules for copying (707) that either say or insinuate that copied cards exist to be cast until the end of the turn and then disappear.

So until when can cards copied by Chun-Li, Countless Kicks be cast?

Edit: changed some wording to be more clear

[Aetherium Slinky]

Usually with an instruction like this you have to do the casting as a part of the resolution of the spell/ability. Look at Mizzix's Mastery, for example - it lets you copy and cast stuff from your grave with a similar wording. Copies of spells can only exist on the stack and there is no mechanic in the game that would let you "store" that copy for later.

704.5e If a copy of a spell is in a zone other than the stack, it ceases to exist. If a copy of a card is in any zone other than the stack or the battlefield, it ceases to exist.

My guess is: you have to cast the copy immediately.