Bridgeport Series II Retrofit & Spindle Speed Question

Hi Everyone,

I just finished converting a Series II to Mach3 control:

Bridgeport Series II CNC Gecko/Mach3 Conversion | The Steampunk Workshop

and am learning how to use it:

Craftsman Compressor Seal Repair - My First CNC Part! | The Steampunk Workshop

My question is this: The spindle goes to 4000 RPM but the part of the speed indicator from 3000 to 4000 RPM is marked in red. Is there limited run time at these speeds? If so, how long?

Thanks!

Jake.