The PauseAdjustedCurrentTime property returns the amount of time (in seconds) since the Screen has started, excluding the amount of time the Screen has been paused.
The following if statement can be used to check if the Screen has been active and unpaused for five seconds:
const float amountOfUnpausedTimeToCheckFor = 5;
if(ScreenManager.CurrentScreen.PausedAdjustedCurrentTime > amountOfUnpausedTimeToCheckFor)
// More than 5 seconds have passed since the Screen was first initialized