Interval Timer Problem

My system frequency is 50MHz and I always start the counter with 0xffff ffff. I think is not important for me to debounce the button because I want to simulate a time mesurement. Later I will get the signal from an external uC.

IF I read the snapL/snapH regs and do:

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zwischen_speicher_vorher = IORD_ALTERA_AVALON_TIMER_SNAPH(SYS_CLK_TIMER_BASE)<<16;

zwischen_speicher_vorher |=IORD_ALTERA_AVALON_TIMER_SNAPL(SYS_CLK_TIMER_BASE);

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then I should get the time of the following calculation:

0xffff ffff - 0xf99cc997

for example. But the solution is too big to be a time in "ms" because the number is something about "1.082139e+08 (ms)". I speak always about "ms" because I adjust it in QSYS for the interval timer.

Now my questions are:

1."Is the time interval different from the adjusted time interval?"

2."Is the calculated number just the count width and not the time? "