1. I leave in a day or so.

2. I leave about in a day.
3. I leave around in a day.
4. I leave roughly in a day.
5. I leave approximately in a day.
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Are they they same in meaning? Do we have some other expressions which mean 'about' as in the sentence here?

#1 is best if you mean to be vague about when you are leaving. The others would be better if you said, "I leave about a day from now", etc. To say "in a day" is quite definite and the adverb seems confusing when used with "in".