Real-time linux can be thought of taking vanilla linux - configuring the kernel in a certain way, booting your kernel with certain boot params and writing your real-time application in a certain way.

While there quite a few hiccups along the way - you will be able to bring down jitter or OS noise to around 1 us. Of course a microkernel based OS like QNX can take you down to around 1 ns - but then the point of using Linux is that you are able to utilize the ecosystem around it.

Look into isolation, real-time patch and high performance computing.