The first event has barely begun when the second already follows
框 · Frame
[clause A] 才 [V/duration]，[subj] 就 [clause B]
觸 · Trigger
You want to say the second thing landed before the first had got under way.
序 · The move
1Put the barely-started event in the first clause, marked with 才.Is this the one that has hardly happened / only just begun?
2Put the event that follows hard on it in the second clause, marked with 就.Does the second arrive sooner than you'd expect from how little the first ran?
3Keep 就 before the verb of its own clause, after that clause's subject.Is 就 hugging the second verb, not floating at the front?
例 · Examples
1我跟他才only just (barely begun)談沒多久not long，他就then already有事先ahead, first離開了。
I'd only just been talking with him a short while when he had something come up and left ahead of me.
Lone 才 says the event came later than expected (他才來 — only now did he come). In 才…就… the 才 means barely-begun, and 就 supplies the sooner-than-expected punch.
我就到家天就下雨了 ✗ → 我才到家，天就下雨了 ✓ (the barely-begun first clause takes 才, not 就).
才下雨一就停了 ✗ → 才下雨就停了 ✓ (don't mix 才 with 一; pick one trigger marker).
我才談沒多久，他離開了 ✗ → 我才談沒多久，他就離開了 ✓ (the second clause keeps 就).
English 'as soon as / no sooner … than' flattens the two events as equally weighted. 才…就… specifically weights the first as scarcely started, so the second feels premature.