Depends on the application.
If I'm using the bacon for breakfast, I'll par cook it and keep it under refrigeration until needed, finishing on the flat top. The exception to this would be on Sunday Brunch, where we fly through it, so I leave it on the counter. It doesn't stay out more than 1/2 hour before serving.
If I'm using it for lunch, for burgers, BLT's, etc., then I cook it until crisp and leave it out at room temp. Once all of the moisture is gone you can leave it out nearly indefinitely with no health issues. Quality issues yes, but not health.