You seem to have posed two questions here, one having to do with discharging a second fire bottle and the other having to do with evacuation based on an on-ground fire
I see no harm in discharging a fire bottle on the ground, seeing as it shuts off the fuel to the engine, causes any air leaks or fire to subside and in most cases will extinguish a real fire confined to a nacelle. At the same time you sure have no need of engine power while stoppd on the ground.
The idea about waiting before discharging a second bottle is to determine if the first one made the problem go away giving one a chance to think what do do next (stick your head out the window, page the crew in the back etc.).
Based on the results of the above, now consider an evacuation.
I'll now take a deep breath and see what others have to say about this.