at any given hour, particularly a time that is late
used for referring to a frequent change from something to another
간헐적으로
그들은 스케줄이 맞을 때마다 가끔 커피를 마시러 만난다.
used for saying that something can only happen on very rare occasions
used for referring to a very special opportunity that most likely will not be offered more than once to someone
in a single action, without delay or hesitation
on multiple occasions
used to describe something that happens at fixed intervals or follows a consistent pattern without fail