During with 〜うちに
Grammar: Time and Sequence » 〜うちに
〜うちに is used to refer to a period of time. The period of time is represented by the modifier in front of うちに. Often 〜うちに is used when taking advantage of an opportunity.
Yukari and her friends have a miscommunication on whether they’ll change from their summer uniforms to their winter uniforms yet. The decision is finalized just in time, as the following day is even colder. Jadeite captures the priestess Rei. Ami uses an ability to fill the area with fog, giving Usagi a chance to act. Jumbo arrives to help Yotsuba and her father move into their new home.Further Reading
Related Grammar
Examples
Decision made during the day yesterday with 〜うちに

Save Rei while it's foggy with 〜うちに

While I didn't see you with 〜うちに
