the purpose of the parameters are described in the MIOS function overview (which unfortunately only comes with assembly examples, this will be changed sooner or later)
So, using small values is not recommented, because in this case the timer will propably more oftenly called then it could execute the appr. code.
I would say, that periods < 100 uS should be prevented, periods > 500 uS should be prefered if the execution of the main program should not be stalled that much.
An example for the timer usage can be found in the “analog box” application, here an excerpt:
// initialize the timer - it should be invoked each mS
MIOS_TIMER_Init(0, 10000); // 1 mS / 100 nS = 10000 cycles
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Yes, the timer should be initialized within Init(), but you are also allowed to change timer period from anywhere else if required (see clockbox -\> dynamic adjustment of BPM)
Best Regards, Thorsten.