After looking at the source code for LWJGL, the function
Sys.getTimerResolution() is potentially different for every operating system. However, currently it is the same on every platform.
This function should not be assumed to be 1000 all the time as not every platform can provide the same time resolution as others (Although currently they do). To support future versions of LWJGL and cross-compatibility, you should use the first example you gave.
You are correct that the two values cancel each other out in the second example but as I said, this is done just in case the game runs on a platform with different time resolution in the future.
Currently, all platform implementations inherit
DefaultSysImplementation which is where the value of 1000 is derived.