Grammar-Quizzes.com gave the following rules that will help us learn how to use ‘during’ and ‘in’

(a) DURING – EMPHASIS ON ACTIVITY DURATION
-During expresses a period or range of time (also, “over”, from X to Y, “throughout”).
ex. We are on vacation during July.
-After a verb that focuses on an activity, “during” is used to indicate a period or range of time for the activity. The meaning of the verb expresses a durative action or state. Using present perfect tense with “during” is awkward.
ex. We had a great time during our stay there.
We had a great time in our stay there. (incorrect)
(b) IN – EMPHASIS ON EXACTLY WHEN
-In specifies a “calendar” time, which may be as small as a moment or as large as a century.
Ex. We are on vacation in July.
-After a verb that focuses on an activity, “in” sounds awkward when indicating a period or range of time for the activity.
Ex. We stayed there in July, not in August.
We stayed there during July, not during August. (incorrect)
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