It's the countdown until the mic switches off again. You may not want to keep the line open all the time, it may prevent your computer from going into power sav

It's the countdown until the mic switches off again. You may not want to keep the line open all the time, it may prevent your computer from going into power saving mode (not sure), and Shazam probably doesn't want everyone to hit their servers constantly either. But if you switch it off and on again the timer starts anew, so it's not a per-user limit.