I am going to recruit some students as our class committee members, and I'm working on editing the new committee obligations now. For some of these duties, they only need to do it once during their term.
Can I describe these works as "Once at a time jobs"? I can not find any reference that explains the meaning and usage of "once at a time". So is it appropriate to use it here?
What do you native speakers normally describe the jobs that you only need to do it once in your lifetime or when you are on duity?
What's more, I used to watch a video clip of Mark Zuckerberg, and his wife said, "Mark, one thing at a time" at the end of the video. What's the meaning of one thing at a time in that video? Is it a warning to Mark that you could only let it happen once, otherwise he will be in trouble?