아까(a-kka, akka)
Refers to a somewhat earlier time today, not immediate past but still recent
When to use
earlier today, hours ago, after lunchtime
The nuance
아까 refers to a past time somewhat earlier than now but not immediately before; it usually indicates a past event earlier today but not just moments ago.
방금(bang-geum, banggeum)
Refers to the immediate past, just a moment ago
When to use
seconds ago, minutes ago, immediate past event
The nuance
방금 indicates something that happened just moments ago, immediately before the current time; the event is very recent.
조금 전(jo-geumjeon, jogeumjeon)
Between 방금 and 아까; more past than 방금 but closer than 아까
When to use
a few minutes ago, just before a meeting, recent past event
The nuance
조금 전 refers to a time slightly earlier than 방금 but more recent than 아까, typically a few to several minutes ago.