A phrase meaning 'now, while you still can' or 'while the time is right' — used to recommend doing something before circumstances change.
今のうちに宿題を終わらせておいたほうがいいよ。
You'd better finish your homework now while you still can.
引っ越すなら今のうちに不用品を処分しておこう。
If you're moving, get rid of unwanted items now (while you can).
寒くなる前に今のうちにタイヤを交換してください。
Please change your tires now, before it gets cold.