count down php/js script

hello guys, i need a php or js script. I can currently upload QR codes manually using my admin panel and this QR code will appear into user side. this QR code will appear instantly for the user without need for him to refresh the pages. I need a count down that will count down on the user side from 40 to 0 seconds starting from the moment i upload the QR code. i have low budget for this. but will give good review