a day or two; in a day or two
Expresses an approximate short duration, typically one or two days. Often used with time-related particles like で or 後に.
This work will probably be finished in a day or two.
I'll contact you again in a day or two.
Means 'a few days', more formal and less specific than 一日か二日.
Compound of 一日 (one day), か (or), and 二日 (two days).