You should explain where to get the library you use...
#include <ARMtimer.h>
Without using a timer to schedule conversions you are at the mercy of other interrupt handlers in the system - this
may or may not be significant in your particular case. You can either just run conversions back-to-back, poll the time
to schedule them, or schedule from a timer interrupt (which is what your code seems to be doing),
Using a timer to schedule allows the rest of your code to proceed with something else at the same time, again this
could be useful - depends on the rest of the sketch...