Learn English – use “once at a time” to describe the following situation

expressionsmeaning-in-context

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?

Best Answer

I've never heard "once at a time" used. Instead you might see your idea expressed with more words, as in: "a duty he/she will need to perform once per shift", "once in each shift" or "once during each shift".

Either a "once-only" or a "one-time" requirement is the best I can come up with for referring to your lifetime as the time period. Otherwise you can use "(only/exactly/at least/at most) once per ______".

On the other hand...

"One thing at a time" means to focus on each thing separately, instead of trying to pay attention to many things in the same moment. It is usually meant to help lessen confusion or stress.

Also note that the phrase "once in a lifetime" usually refers to opportunities, not obligations, so it would be confusing if used here.

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