after a while
after a while {informal} or in a while {adv. phr.}
Later, at some time in the future; after a time that is not short and not long.
"Dad, will you help me make this model plane?" "After a while, Jimmy, when I finish reading the newspaper."
The boys gathered some wood, and in a while, a hot fire was burning.
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Source: A Dictionary of American Idioms