count for exact time

Hi

I made a counter with USB-6343 as following :

Delay decides how much time does it count.

when I run this vi with 1000hz input for 1000ms, it counts not only 1000 but also 1001, 1002, 1003.

It seems to count for not 1000ms but 1001ms or something.

I found a document about Real-Time OS or FPGA, but I'm using a USB-6343 in window10, so It's not help for me.

is there any tip for measuring a count in exact time(about 0.1ms or less) with USB-6343 and window10 OS?

thanks.