Visible change takes 8 to 12 weeks of consistent training plus a calorie deficit. Not a perfect 12 weeks, a consistent one.
There's no spot reduction. Fat comes off the whole body, and the lower belly is usually the last place to go. Doing more ab work doesn't change that.
Track it properly: progress photos and measurements every 2 to 4 weeks, and how your clothes fit. The scale is the worst measure, because you're building muscle while you lose fat.