This script provides working(not perfect) shooting range. You can try it with /poligon command but if you want to add it to your server. You should edit it a bit.
Random target spawn points.
Changing interval between targets.
20 - 45 targets left: 3000 ms
10 - 20 targets left: 2500 ms
0 - 10 targets left: 2000 ms
Points based on hit area (not working perfect)
Script testing video